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Our lab director discusses research exploring the relationship between caffeine and physiological and psychological responses in adolescents.

REVIEW article

The safety of ingested caffeine: a comprehensive review.

• 1 Department of Exercise and Nutrition Sciences, University at Buffalo, Buffalo, NY, USA
• 2 Department of Community Health and Health Behavior, University at Buffalo, Buffalo, NY, USA
• 3 Aix Marseille Univ, INSERM, INS, Inst Neurosci Syst, Marseille, France
• 4 Wayne State University School of Medicine, Children’s Hospital of Michigan, Detroit, MI, USA

Caffeine is the most widely consumed psychoactive drug in the world. Natural sources of caffeine include coffee, tea, and chocolate. Synthetic caffeine is also added to products to promote arousal, alertness, energy, and elevated mood. Over the past decade, the introduction of new caffeine-containing food products, as well as changes in consumption patterns of the more traditional sources of caffeine, has increased scrutiny by health authorities and regulatory bodies about the overall consumption of caffeine and its potential cumulative effects on behavior and physiology. Of particular concern is the rate of caffeine intake among populations potentially vulnerable to the negative effects of caffeine consumption: pregnant and lactating women, children and adolescents, young adults, and people with underlying heart or other health conditions, such as mental illness. Here, we review the research into the safety and safe doses of ingested caffeine in healthy and in vulnerable populations. We report that, for healthy adults, caffeine consumption is relatively safe, but that for some vulnerable populations, caffeine consumption could be harmful, including impairments in cardiovascular function, sleep, and substance use. We also identified several gaps in the literature on which we based recommendations for the future of caffeine research.

Introduction

Caffeine is the most widely consumed psychoactive drug in the world ( 1 ) and one of the most comprehensively studied ingredients in the food supply. It occurs naturally in the leaves and seeds of many plants and has a taste bitter enough to deter pests ( 2 ). Natural sources of dietary caffeine include coffee, tea, and chocolate. Synthetic caffeine is also added to products to enhance their stimulant properties. Historically, this addition was limited to soda-type beverages, but over the past decade, caffeine has been added to a diverse variety of foods and non-food items to promote arousal, alertness, energy, and elevated mood ( 3 – 5 ). This recent increase in caffeine-containing food products, as well as changes in patterns of consumption of the more traditional sources of caffeine, has increased scrutiny by health authorities and regulatory bodies of the overall consumption of caffeine and its potential cumulative effects on behavior and physiology. Of particular concern is the rate of caffeine intake among populations potentially vulnerable to its negative effects. Health and regulatory authorities have recently highlighted the risk of consumption among pregnant and lactating women, children, adolescents, young adults, and people with underlying heart and other health conditions.

In light of these concerns, we conducted a comprehensive review of all relevant published clinical and intervention trials, observational studies, systematic reviews, meta-analyses, and expert reviews on the use and safety of caffeine in humans, complemented where needed (e.g., for aspects of safety or mechanisms of action) with evidence from animal studies. We evaluated the strengths and limitations of the evidence on the safety of ingested caffeine, specifically focusing on the safety of caffeine-containing foods (e.g., beverages and solid foods). We summarize here what is known and what remains to be learned about caffeine intake and safety in healthy and vulnerable populations and highlight needed research.

Dietary Sources of Caffeine

Adults commonly consume caffeine in coffee and tea, both of which contain natural caffeine in their leaves or beans ( 6 ). Energy drinks often contain caffeine from natural products such as extracts from guarana leaves. In addition to coffee, tea, and energy drinks, caffeine is also naturally present in cocoa beans and thus in chocolate. The amount of caffeine in chocolate varies by the percentage of cocoa it contains, with 100% cocoa chocolate (unsweetened baking chocolate) containing around 240 mg caffeine/100 g, 55% cocoa (bittersweet) containing 124 mg caffeine/100 g, and 33% cocoa (milk chocolate) containing 45 mg caffeine/100 g ( 7 ). Synthetic caffeine is also added to soda and energy drinks ( 8 ), which are commonly consumed by children and adolescents worldwide, and to other food and non-food products with niche markets for subsets of consumers, such as juice, chewing gum, water, cookies, hot sauce, candy, beef jerky, mints, syrup, waffles, shampoo, soap, lip balm, eye cream, body scrub, and body lotion. These products are primarily marketed with claims that they provide energy, alertness, or are “age-defying.” Last year, the FDA announced that it will begin investigating the safety of caffeine added to food products, with a special emphasis on children and adolescents. 1

Caffeine is a constituent of many over-the-counter pain relievers and prescription drugs because the vasoconstricting and anti-inflammatory effects of caffeine act as a compliment to analgesics, in some cases increasing the effectiveness of pain relievers by up to 40% ( 9 – 14 ). Caffeine is used for general pain relief in medications such as Midol™ and Vanquis™, which contain doses ranging from 33 to 60 mg. It is used therapeutically in combination with ergotamine to treat migraine headaches and in combination with non-steroidal anti-inflammatory analgesics. Anacin™, Excedrin™, Goody’s™ headache powder, and pain reliever plus contain between 32 and 65 mg of caffeine, and prescription headache medications, including Fiorinal, Orphenadrine, and Synalgos, contain between 30 and 60 mg of caffeine.

Alone, caffeine is used as a somnolytic to counteract drowsiness (e.g., NoDoze™ and Vivarin™ each contain 200 mg of caffeine), to enhance seizure duration in electroconvulsive therapy, and to treat respiratory depression in neonates, postprandial hypotension, and obesity ( 15 – 18 ). Similar synergistic additive effects of caffeine and medications also occur in treatments for asthma and gall bladder disease, attention deficit-hyperactivity disorder, shortness-of-breath in newborns, low blood pressure, and weight loss ( 19 – 24 ). Between 50 and 200 mg of caffeine is added to some weight-loss supplements (Dexatrim™, Hydroxycut™, and Nutrisystem™ Energi-Zing Shake) for its purported effects on appetite suppression and increased metabolism ( 25 ).

Estimates of Caffeine Consumption

Recent estimates in adults suggest that more than 85% of adults in the U.S. regularly consume caffeine, with an average daily intake of about 180 mg/day, about the amount of caffeine in up to two cups of coffee ( 6 , 26 ). Among children and adolescents, caffeine use appears to be either stable or slightly decreasing over time, despite the influx of new caffeine-containing products on the market. For example, a study by Ahluwalia and Herrick using NHANES data reports that about 75% of U.S. children between 6 and 19 years old consume caffeine, with an average consumption of 25 mg/day in children 2–11 years old and 50 mg/day in children 12–17 years old ( 8 ). Another study also using the NHANES dataset reports average caffeine consumption in children and adolescents as 35 mg/day, with 4–8 years old consuming 15 mg/day, 9–13 years old consuming 26 mg/day, and 14–19 years old consuming 61 mg/day ( 27 ).

Coffee consumption varies worldwide: Finland and Norway are at the top of the list, with averages of 9.6 and 7.2 kg of coffee consumed per capita per year. The U.S. ranks 22nd, with 3.1 kg. A 1984 study showed that Canada and the U.S. had per capita rates of caffeine consumption that were triple the worldwide average but that were still half of what was consumed in countries such as Sweden and the United Kingdom (U.K.) ( 28 ). A more recent study from the Canadian Community Health Survey found that coffee was the second most popular drink among Canadian adults, with water being the first ( 29 ). The U.K.’s National Diet and Nutrition Survey also collected information on caffeine consumption through foods and beverages from adults and children. These data show that, on average, adults in the U.K. consume about 130 mg/day of caffeine and that children consume about 35 mg/day ( 30 ). A study from Japan using 4-day food diaries reported average daily caffeine consumption as about 260 mg/day in adults ( 31 ). Finally, people in Finland, Norway, the Netherlands, and Sweden are consistently reported to drink the most caffeine, primarily from coffee. However, these estimates are derived from sales of coffee and not from surveys of individual intake.

Trends in Caffeine Consumption

Trends in caffeine consumption have been stable among adults for the past two decades ( 6 ). Among children aged 2–19 years old, caffeine consumption increased significantly from the 1970s through the 1990s ( 5 , 32 ). This increase was also marked by a decrease in dairy consumption and an increase in soda consumption ( 32 ). More recent data suggest that caffeine consumption has remained stable among this age group since the 1990s ( 8 , 33 ), a finding similar to that in adults. This stability is somewhat surprising, given the marked increase in the number, variety, and availability of caffeinated beverages introduced in the past decade. Some researchers speculate that this stability reflects a lag in data collection or in consumption trends from when products are introduced to the market to when data are collected (for example, the most recent NHANES data on caffeine consumption are from 2011). Another potential explanation is that a possible decline in consumption among younger children has been offset by increased consumption among older adolescents and young adults attracted to the increasing number of new caffeine-containing products. Targeted marketing strategies seem to support this explanation. Advertisements for caffeinated energy drinks, the fastest growing segment of the beverage market ( 34 , 35 ), are specifically aimed at adolescent and young adult males ( 36 , 37 ). Given the popularity and prevalence of energy drinks, caffeine consumption could reasonably be expected to increase quickly among children and adolescents.

Caffeine intake usually begins in childhood, most often in the form of chocolate, soda, and chocolate milk ( 8 ). As children become adolescents, they increase consumption of soda and begin to add beverages with greater caffeine content, such as coffee and energy drinks ( 8 ). Average caffeine intakes increase from about 50 mg/day in childhood (aged 2–11 years) to 180 mg/day in adulthood ( 6 ). This amount is about 2 mg/kg/day in children, 2.4 mg/kg/day in women, and 2.0 mg/kg/day in men. This shift in absolute caffeine intake from childhood to adulthood is related to changes in the pattern of consumption, with adults adopting a more regular, daily pattern of consumption relative to children ( 6 ). In addition, the dietary sources of caffeine shift over the lifespan: adults primarily consume coffee and tea, whereas children and adolescents consume primarily soda and chocolate, which contain much lower amounts of caffeine.

The pattern of caffeine use changes across the lifespan has not been studied, but tolerance to the effects of caffeine has been speculated to increase the desire for larger doses to reverse the impact of overnight caffeine withdrawal ( 38 ). In addition, once caffeine intake is great enough to disrupt sleep, or if sleep duration is shortened by other factors, caffeine is often used to promote morning arousal, which can further disrupt sleep, creating a pattern in which caffeine is both the cause and the cure for too little sleep ( 38 , 39 ). Variations in caffeine sensitivity and consumption may relate to polymorphisms in enzymes that degrade caffeine and in adenosine receptors, which are the primary targets of caffeine ( 40 ).

The Pharmacokinetics of Caffeine

Caffeine works by binding to adenosine receptors located in the central and peripheral nervous systems as well as in various organs, such as the heart, and blood vessels. Adenosine is a molecule involved in numerous biochemical pathways, mostly for energy transfer (in the form of adenosine triphosphate, the basic fuel of cells) and signaling. Adenosine is a neuromodulator that can promote sleep, affect memory and learning, and protect cells after insults. Adenosine can also act on several types of cognate receptors: for example, A1, A2a, A2b, and A3, which are G-coupled proteins. In the central nervous system, activating A1 receptors inhibits the release of neurotransmitters, whereas activating A2a receptors promotes their release ( 41 ). During early stages of brain development, the predominant effect of caffeine is to antagonize type 2A adenosine receptors, slowing down the migration speed of some neurons ( 42 ). At toxic doses (i.e., extreme doses that humans rarely absorb), caffeine can alter other cellular functions, releasing Ca 2+ from intracellular stores at lethal levels ( 43 ). The toxic dose effects are not considered here because, although they are of great concern to the medical profession and may be on the rise, they are still rare compared to other, non-lethal caffeine effects and the precise mechanism of caffeine toxicity has not been investigated in humans.

Absorption and Metabolism

Caffeine is usually ingested. Caffeine is soluble in water and lipids, easily crosses the blood–brain barrier, and can be found in all body fluids, including saliva and cerebrospinal fluid. Importantly, caffeine ingested by women perinatally will be present in the umbilical cord and breast milk. Hence, it will also be present in the fetus and in breastfed infants. Caffeine is absorbed rapidly and totally in the small intestine in less than 1 h ( 44 ) and diffuses rapidly in other tissues ( 45 ). Absorption by the small intestine does not seem to vary by sex, genetic background, environmental factors, or other variables ( 46 ), although specific studies are still needed to confirm this premise. Caffeine concentrations peak in saliva 45 min after ingestion ( 47 ) and in serum after about 2 h ( 48 ). Caffeine has a relatively long half-life of 3–7 h in adults. In neonates, the half-life is even longer—between 65 and 130 h—because of their immature kidneys and liver. Peak concentrations are important because the effects of caffeine depend in part on the length of time it remains in tissues. Clearly, the effects are age dependent and depend on complex genetic and environmental interactions.

Caffeine is primarily metabolized in the liver by the cytochrome P450 oxidase enzyme system; in particular, by the CYP1A2 enzyme. However, this oxidase enzyme system is also present in other tissues, including the brain ( 49 ). Caffeine metabolism is affected by several factors, described in detail below.

Genetic Variation

The CYP1A2 gene, which encodes for a cytochrome P450 enzyme, has a large genetic variability. At least 150 single-nucleotide polymorphisms can accelerate caffeine clearance ( 50 ). The metabolic consequences of this polymorphism on caffeine downstream effects should be studied in humans. Genetic variation (i.e., increased or decreased activity of the cytochrome P450 oxidase enzyme) may increase or decrease the possible harmful effects of caffeine (e.g., during pregnancy) and any beneficial effects (e.g., on memory and learning during aging or in pathologies, such as Alzheimer’s disease). The half-life of caffeine may also be increased in liver diseases, which decreases P450 activity ( 50 ).

The molecular targets of caffeine, namely the adenosine receptors, also have great genetic variability. For example, common variants of the gene encoding for the A2a receptor can disrupt sleep ( 51 ) or cause anxiety in some individuals ( 52 ) after ingesting caffeine. More studies are needed to determine the effects of genetic variants on the consequences of caffeine consumption ( 53 ), not only in the central nervous system but also in other organs, such as the heart ( 40 ).

Circadian Rhythms

The expression of the cytochrome P450 epoxygenases is regulated in a circadian manner ( 54 ). Although this effect was discovered in cultured rodent cells, it may apply to many species, including humans ( 55 ). The implications are particularly important because the effects of caffeine (at least the duration of its activity) will differ during the circadian cycle. Because caffeine can alter sleep, it may also change the circadian rhythm, leading to a change in expression patterns for the cytochrome P450. One interesting hypothesis is whether caffeine consumption in adolescents and adults disrupts the expression of P450 in relation to its circadian rhythm. If the expression is downregulated, the effects of caffeine could be prolonged and produce a negative feedback loop.

Steroid Hormones

The cytochrome P450 oxidase enzyme system is the same enzyme that metabolizes steroid hormones ( 56 ). Thus, steroid hormones slow caffeine metabolism. In women, this effect slows the metabolism of caffeine during pregnancy and when taking oral contraceptives ( 57 ). However, studies have not found marked differences in caffeine metabolism between the luteal and follicular phases of the menstrual cycle ( 57 , 58 ). Oral contraceptives tend to double the half-life of caffeine ( 59 ).

The half-life of caffeine is on average 8.3 h longer during pregnancy and may be as much as 16 h longer than usual ( 60 , 61 ). This longer half-life means that the effects of caffeine will be longer lasting in women and in the fetus. Given the effects that caffeine may have on brain development, this increased half-life in pregnant women should be taken into account when considering safety issues.

Caffeine is eliminated more slowly during early infancy, requiring perhaps 80 h in preterm and healthy-term neonates, because of the reduced efficiency of cytochrome P450 ( 62 , 63 ). Elimination is likely to be at least as slow in the fetus. Fetal exposure to caffeine during pregnancy may potentially have long-lasting effects, especially in the brain. By age 6 months, infants eliminate caffeine at the same rate as that of adults ( 62 ).

Substance Use

Cigarette smoking doubles the rate of caffeine clearance by increasing liver enzyme activity, which may explain the higher rate of caffeine consumption among smokers ( 64 ). Substantial alcohol intake increases the half-life of caffeine and decreases its clearance ( 65 ).

Central and Peripheral Effects of Caffeine

The general effects of caffeine on body functions are summarized in Table 1 .

Table 1. Summary of outcome measures investigated .

Cognitive Effects

Caffeine can influence objective and perceived cognitive performance by increasing alertness and wakefulness ( 66 – 68 ). Acute caffeine can also improve performance on memory tasks ( 69 , 70 ). Finally, caffeine improves psychomotor vigilance, such as reaction time ( 71 – 73 ). The impact of caffeine appears to be greater under conditions that would negatively impact performance, such as acute caffeine withdrawal ( 74 – 76 ) or sleep deprivation ( 71 , 77 ). In fact, studies that have employed long-term caffeine withdrawal methodology have consistently failed to find cognitive enhancing effects of acute caffeine ( 78 – 82 ). Nevertheless, in 2001, the Institute of Medicine’s Food and Nutrition Board Committee on Military Nutrition Research reported that ingesting 150 mg of caffeine enhances cognitive performance for at least 10 h ( 83 ), and this recommendation has not been updated in light of more recent empirical findings.

Numerous preclinical studies have found that antagonizing adenosine receptors, including with caffeine, has neuroprotective effects during aging and in neurological disorders by slowing cognitive decline and the progression of the disorders [reviewed in Ref. ( 84 , 85 )]. Based on these animal studies, several large longitudinal clinical studies in different countries have established an inverse relationship between coffee consumption and memory decline during normal aging ( 86 – 88 ). However, a study of 4,200 women and 1,800 men reported that caffeine consumption reduced cognitive decline only in women ( 69 ). In addition, a more recent study in a small group of women ( 89 ) failed to replicate the findings of the Ritchie study, demonstrating that more work is needed to understand the relationship between habitual caffeine consumption and cognitive performance. Finally, large cohort studies of men and women have also found an inverse relationship between caffeine consumption and the risk of Parkinson’s disease ( 90 – 92 ) and Alzheimer’s disease ( 93 – 95 ).

Pain Relief

Caffeine has long been used to treat pain. However, its pain-reduction effects were not properly studied until 1984, when Lachance ( 96 ) documented that additive caffeine reduced the dose of acetaminophen necessary to achieve the target of a 40% reduction in pain scores ( 96 ). Since then, the vasoconstricting action of caffeine, secondary to adenosine receptor antagonism, has been associated with pain relief ( 97 ). Several studies have reported that acute dietary caffeine consumption can reduce pain ( 98 , 99 ). In addition, caffeine in doses of between 300 and 500 mg can soothe post-dural puncture headaches, which is the most common complication of lumbar puncture procedures ( 100 ).

Cardiovascular Effects

In general, acute intake of caffeine stimulates a modest increase in blood pressure (both systolic and diastolic), effects on heart rate (bradycardia or tachycardia, depending on dose), and neuroendocrine effects (release of epinephrine, norepinephrine, and renin) ( 101 ). These effects suggest that the mechanism of action is an increase in intracellular calcium concentrations, the release of norepinephrine, and the sensitization of dopamine receptors. These events may lead to supraventricular and ventricular tachyarrhythmias, especially at high doses. One proposed mechanism for caffeine-related cardiac arrhythmias is, again, the blockade of adenosine receptors ( 102 , 103 ).

Patients with cardiac disease are often warned about the potential harmful effects of caffeine. For example, 94% of several hundred physicians from Minnesota and Vermont recommended reducing or stopping caffeine for patients reporting heart palpitations ( 104 ). However, this advice has been based primarily on anecdote and folklore ( 105 , 106 ). Many of caffeine’s health effects occur after sympathetic excitation. Today, however, data suggest that caffeine does have cardiac effects, and arrhythmia is among them ( 107 ). Moreover, effects that do exist differ by dose and between habitual and non-habitual users. This severity of these threats often depends on such factors as preexisting medical conditions as well as the quantity of the ingredients taken and the length of time a person has been exposed to these substances. Many of the ingredients that include caffeine alone or in combination with other active substances have the potential to interact with prescription and over-the-counter medications. At typical caffeine doses, however, studies have documented mild changes in heart rate and blood pressure, a slight increase in sympathetic activity, and small changes in cardiac electrophysiological properties ( 105 , 108 – 110 ).

Vascular System Effects

Caffeine is believed to improve endothelial cell function at rest by increasing intracellular calcium concentrations, which stimulates the expression of endothelial nitric oxide synthase, which in turn stimulates the endothelial cells to produce nitric oxide. The nitric oxide then diffuses into vascular smooth muscle, which lies just underneath the endothelial cells, causing vasodilation ( 111 ). Caffeine can also bind directly to the vascular smooth muscle cell receptors and, through similar mechanisms, cause vasoconstriction ( 112 ).

The above information not withstanding, consuming caffeine immediately before or during exercise can be harmful and may increase the risk for myocardial ischemia ( 113 ). Indirect laboratory measures indicate that caffeine consumed immediately before exercising substantially reduces myocardial blood flow in healthy individuals ( 114 ). Several mechanisms may explain this reduction ( 114 ), including the ability of caffeine to block adenosine receptors that modulate coronary vasomotor tone. This vasoconstrictive effect might be more pronounced among caffeine-naïve individuals or in those who quickly ingest higher amounts of caffeine: for example, by consuming energy drinks. When caffeine blocks adenosine receptors, it reduces the ability of the coronary arteries to improve their flow commensurate with the increased myocardial demand of exercise, which could result in supply demand ischemia ( 114 ).

Caffeine Toxicity

Seifert et al. ( 115 ) examined data from calls to the U.S. National Poison Data System made between October 1, 2010 and September 30, 2011 related to caffeine exposure and energy drink consumption ( 115 ). Of 2.3 million calls, 4,854 (0.2%) were energy drink related. Of the 1,480 calls related to exposures not involving alcohol, 51% concerned children under the age of 6, and 77% were the result of unintentional ingestion. The overall incidence of moderate-to-major adverse effects of energy drink-related toxicity was 15.2% for non-alcoholic energy drinks. The seven cases with major adverse effects consisted of three with seizure, two with non-ventricular dysrhythmia, one with ventricular dysrhythmia, and one with tachypnea. Of the same 1,480 calls, 946 concerned products containing caffeine only and 534 concerned products with caffeine-containing additives, such as guarana (a plant whose seeds are high in caffeine) or taurine (a naturally occurring organic acid often used as a nutritional supplement). Compared to energy drinks with additives, caffeine-only exposures involved a significantly greater proportion of cases less than 6 years old (50.7%) and a greater proportion of unintentional exposures (76.7%). The proportion of cases involving additives referred to a health-care facility was also significantly greater, as was the incidence of toxic effects of any severity. One caveat to this study is that information on preexisting medical conditions was not available for the cases studied. Research in this area should attempt to include and account for preexisting health conditions.

Researchers have also expressed concern about unintentional caffeine consumption and an increase in overconsumption of caffeinated energy drinks in children and young adults. For example, Bronstein et al. ( 116 ) identified 48,177 poison center calls related to caffeine consumption and 6,724 calls related specifically to energy drink consumption. Seifert et al. ( 115 ) also reported that 55% of calls regarding caffeine consumption were related to unintentional exposures ( 115 , 116 ). A study of 13- to 17-year olds admitted to urban emergency rooms in the U.S. found that more than half reported consuming energy drinks in the past month, and those who had were also more likely to report that they had “gotten into trouble at home, school, or work” than those who consumed other types of caffeinated beverages [OR: 3.12 (1.24–7.88)] ( 117 ).

In March 2013, 18 scientific and medical experts sent the FDA commissioner a report summarizing the research findings on energy drink consumption in children. This report concluded “… there is neither sufficient evidence of safety nor a consensus of scientific opinion to conclude that the high levels of added caffeine in energy drinks are safe under the conditions of their intended use, as required by the FDA’s Generally Recognized As Safe standards for food additives. To the contrary, the best available scientific evidence demonstrates a robust correlation between the caffeine levels in energy drinks and adverse health and safety consequences, particularly among children, adolescents, and young adults” ( 118 ). Furthermore, the Institute of Medicine has recommended that drinks containing caffeine should not be sold to children at school ( 119 ). In addition, The American Academy of Pediatrics’ Committee on Nutrition and the Council on Sports Medicine and Fitness recently concluded that “rigorous review and analysis of the literature reveal that caffeine and other stimulant substances contained in energy drinks have no place in the diet of children and adolescents” ( 120 ).

Death from caffeine ingestion appears to be rare. This rarity may be related, in part, to the marked gastric irritation from caffeine that results in spontaneous emesis. Nevertheless, several hospitalizations and some deaths from caffeine toxicity have been reported ( 121 ). For example, between 2005 and 2011, there were 79,438 emergency room visits attributable to overconsumption of energy products containing high levels of caffeine in patients aged 12 years and older ( 121 ). In most of these cases, the mechanism seems to be tachyarrhythmia and involves unusually high doses of caffeine (>3 mg/kg) ( 121 ). Most deaths after caffeine intoxication were caused by overdoses of diet pills and stimulants, and most have occurred in young patients without known underlying heart disease or any variant of normal, such as mitral valve prolapse. In one non-fatal adverse event report, no predisposing factors or structural cardiac abnormality were associated with atrial fibrillation ( 122 ). In this case, caffeine-induced atrial fibrillation spontaneously reverted to normal sinus rhythm.

Reproductive Effects

Caffeine consumption is associated with fertility indices in some studies but not in others. An extensive literature review by the Oak Ridge National Laboratory concluded that chronic caffeine intake in humans is related to adverse effects on conception and reproduction, such as delayed conception and decreased fecundity. These effects appeared at caffeine doses above 200 mg/day ( 121 ). A separate review concluded that for healthy adults, intakes below 400 mg/day were not associated with adverse reproductive effects; however, the authors recommended consumption below 300 mg/day for women of reproductive age ( 123 ). In addition, some researchers argue that any association between caffeine intake and reproductive outcomes may be explained by other variables, such as maternal smoking or substance use and that research should address confounding, as well as errors in measuring exposure ( 124 ).

Reports regarding caffeine consumption and spontaneous abortions have also been conflicting. Weng et al. ( 125 ) reported a hazard ratio of 2.23 for spontaneous abortion among 164 women who consumed 200 mg/day or more of caffeine and of 1.34 for 899 women who consumed less than 200 mg/day ( 125 ). After adjusting for pregnancy symptoms, such as nausea and vomiting, other researchers found that consuming doses of 200 mg/day or more still almost doubled the risk of spontaneous abortion. A meta-analysis by Chen et al. ( 126 ) reported that, compared to a no or very low caffeine intake reference group (0–50 mg/day during pregnancy), every additional 100 mg/day of caffeine (about the amount contained in a typical cup of coffee) increased the risk of pregnancy loss (both miscarriage and stillbirth) by 7% ( 126 ). In addition, among women consuming more than 700 mg/day, the risk of pregnancy loss was increased by 72%. Similar findings were reported by Li et al. ( 127 ), who found in a separate meta-analysis of 26 studies that the risk of pregnancy loss increased by 19% for every additional 150 mg of caffeine consumed per day and by 8% for every additional 2 cups of coffee (about 200 mg) per day ( 127 ). However, Savitz et al. ( 128 ) reported no association among 2407 women who were interviewed regarding caffeine intake before experiencing spontaneous abortion ( 128 ). This finding suggests that recall bias may explain the increased hazards of spontaneous abortion reported by Weng et al. ( 125 ) and potentially other researchers ( 125 ). Other comprehensive reviews have reported some evidence that caffeine intakes of more than 300 mg/day have been associated with spontaneous abortion and low birth weight, but all have stressed the need for further research before a causal relationship can be established ( 129 , 130 ). A recent study from the Nurses Health Study shows pre-pregnancy coffee consumption at levels ≥4 serving/day is associated with an increased risk of spontaneous abortions, particularly at 8–19 weeks gestational age ( 131 ).

Congenital Anomalies

No clear association has been found in humans between moderate doses of caffeine ingestion during pregnancy and birth defects, including congenital heart disease ( 132 ). For example, the National Birth Defects Prevention Study found variable results for this possible association ( 133 ). In another study of 2,030 malformed infants, the risk of congenital anomalies was not related to the total maternal daily caffeine ingestion below 400 mg/day (or up to 4 cups of coffee) during pregnancy ( 134 ). Other studies have found that the frequency of all congenital malformations, including congenital heart defects, was no higher than expected among women who drank between four and eight cups of coffee daily during their pregnancy ( 135 , 136 ). The Institute of Medicine’s Workshop on Potential Health Hazards Associated with Consumption of Caffeine in Food and Dietary Supplements found that risk of congenital defects from caffeine was not increased in the range of amounts women typically consumed during pregnancy ( 121 ).

The consequences of caffeine consumption during pregnancy on offspring have recently been studied in mice ( 137 ). Caffeine consumption by the dam (the human equivalent of two to three cups of coffee per day) was associated with caffeine concentrations in the offspring brain that were similar to those in the umbilical cords of women drinking two to three cups of coffee per day ( 138 ). At early stages of development, specific types of neurons arise in particular brain regions and then migrate to their target areas. Caffeine slowed the migration of these neurons by 50% by antagonizing adenosine type 2A receptors. As a result, these neurons were late at being incorporated into the circuitry, with negative consequences: pups were more susceptible to seizures, and in adulthood, in utero exposed mice had mild cognitive deficits. This study was the first to document that caffeine exposure during pregnancy could harm the offspring. Generalizing the results of animal studies to humans is always speculative, but these results strongly justify conducting prospective studies in humans. Interestingly, in keeping with animal data, greater exposure to caffeine during pregnancy is associated with a lower IQ in children at age 5.5 years ( 139 ). This finding again supports the need for additional studies in humans.

Birth Weight Effects

Several studies have reported a significant negative association between maternal caffeine consumption and birth weight ( 84 , 85 , 140 – 142 ). However, two other large prospective cohort studies reported a dose-dependent positive association between caffeine intake during pregnancy and the risk of adverse birth weight-related outcomes, such as fetal growth restriction and small for gestational age babies ( 143 , 144 ). In these studies, caffeine intake and adverse birth weight-related outcomes were found at all amounts of maternal caffeine intake. In both studies, the risk for adverse birth-related outcomes increased notably at a caffeine dose of 200 mg/day from all nutritional sources. In addition, one study of 1,207 pregnant women reported that, although they tended to reduce consumption of caffeine during pregnancy, a moderate decrease in caffeine intake to 100 mg/day in the third trimester of pregnancy did not decrease the risk of adverse birth weight-related outcomes ( 145 ).

Two separate meta-analyses of different sets of studies by Rhee et al. ( 142 ) and Chen et al. ( 146 ) reported odds ratios of having a newborn classified as low-birth weight (less than 2,500 g) for maternal caffeine consumption above 50 mg/day when compared to intakes below 50 mg/day. Furthermore, both meta-analyses found an increased risk of low-birth weight offspring for every 100 mg/day increase in maternal caffeine consumption (OR, 1.03–1.62). Another study by Hoyt et al. ( 140 ) found the odds ratios of having a low-birth weight baby increased to a range of 1.3–2.1 in women consuming more than 300 mg/day of caffeine during pregnancy ( 140 ).

Taken together, these studies provide substantial evidence of a negative association between maternal caffeine consumption and infant birth weight. Even so, the studies all relied on maternal self-report about caffeine intake; thus, the data may not be accurate. Furthermore, it is possible that additional variables, not controlled for in the analyses, could explain these relationships. For example, chronic sleep loss during pregnancy is also associated with poor birth outcomes, including low birth weight ( 147 ). Thus, pregnant women with disrupted sleep might use more caffeine to increase alertness, so the impact on birth weight could be related to short sleep duration and not to caffeine. Although this conclusion is speculative, it highlights the importance of considering additional variables when interpreting correlational data.

Caffeine may cause irritability and sleep disruption in nursing infants whose mothers consume caffeine ( 148 ), but the findings are equivocal ( 149 ). In addition, some evidence indicates that caffeine intake can reduce production of breast milk ( 148 ). Mothers are often advised by their doctors to reduce or eliminate caffeine intake if they feel that their infant shows signs of caffeine sensitivity, but there is no evidence in the literature of detrimental effects of caffeine ingestion during lactation in the general population. Behavioral issues, such as fussiness, jitteriness, and poor sleep patterns, have been reported among infants breastfed by mothers who consumed 10 or more cups of coffee (~1 g of caffeine) per day ( 121 ). The effects of caffeine in breast milk can be amplified in preterm infants or infants less than 5 months old because they metabolize caffeine so slowly ( 121 ). In addition, an intake of more than 450 mL (about two cups) of coffee per day may decrease breast milk iron concentrations, which could contribute to infant anemia ( 150 ). However, the European Food Safety Authority concluded that a single dose of 200 mg or less of caffeine (about two cups) consumed by lactating women, as well as chronic intakes at or below 200 mg, pose no safety concerns for breastfed infants ( 151 ).

Outcomes after Infancy

Few studies have examined the impact of maternal caffeine intake on outcomes after infancy. One study by Klebanoff and Keim ( 152 , 153 ) using 2,197 mother–child dyads measured child IQ and problem behaviors and examined correlations with maternal paraxanthine concentrations (a metabolite of caffeine) taken between 20 and 26 weeks of gestation ( 152 , 153 ). This study found no meaningful relationship between maternal caffeine intake during pregnancy and a range of behavioral and cognitive measures in children 4–7 years old. However, another study of 1,083 mother–child pairs revealed that children who were born to mothers who estimated caffeine intake >200 mg/day during pregnancy had an odds ratio of 2.3 (95% confidence interval of 1.13–4.69) of having a child with a lower IQ at age of 5.5 years compared to the reference population of mothers reporting <100 mg/day of caffeine consumption ( 139 ). A study by Li et al. ( 154 ) reported that maternal caffeine intake was associated with increased odds of childhood obesity, with each 100-mg increase in daily maternal caffeine intake being associated with a 23% higher odds of obesity at age 15 years ( 127 ), although a study by Klebanoff and Keim found no relationships between maternal caffeine consumption and childhood obesity ( 152 , 153 ).

The above studies are correlational; thus, causation cannot be determined. In addition, the maternal caffeine intake in these studies was estimated based on self-reports. One potential explanation for the discrepancies described above is the method used to determine caffeine use. In the study by Klebanoff and Keim ( 152 , 153 ), which found no significant relationship between maternal caffeine intake and outcomes after infancy, measured serum caffeine concentrations and did not use self-report ( 152 , 153 ). By contrast, the studies that found significant relationships between maternal intake and measures in the offspring after infancy relied exclusively on retrospective self-reports, several years after the fact, about prenatal caffeine consumption by mothers after they gave birth and during the first two trimesters of pregnancy, respectively. Caffeine intake was estimated from food-frequency questionnaires or interviews in which women reported how often and how much they consumed coffee, tea, and soda. Other variables affecting self-reported caffeine consumption and offspring behavioral outcomes might explain these relationships, but in the study that relied entirely on serum concentrations, such variables were not identified. These studies also measured different outcomes in the offspring. Klebanoff and Keim ( 152 , 153 ) had the most comprehensive battery of cognitive and behavioral outcomes, but Galera et al. ( 139 ) only measured IQ (The Wechsler Preschool and Primary Scale of Intelligence Third Edition), and Li et al. ( 127 ) only measured weight and weight gain in the offspring ( 139 , 152 – 154 ). Meaningful comparisons of studies are difficult when the methods for assessing caffeine intake and the outcomes are different. Research with objective measures of caffeine intake and standard outcomes is needed.

Other Existent, Emerging, or Minor Issues

Most of the research examining linkages between caffeine and cancer has been conducted on coffee and tea and not on caffeine specifically, which makes it difficult to determine the mechanism. The International Agency for Research on Cancer has concluded that the evidence is insufficient to conclude that caffeine, as consumed by a typical coffee drinker, is carcinogenic ( 121 ). Several large prospective trials have reached the same conclusion ( 123 , 155 , 156 ). Furthermore, Nawrot et al. ( 123 ) concluded in their review of the research that caffeine is unlikely to be a human carcinogen at levels less than 500 mg/day, to the equivalent of five cups of coffee ( 123 ).

Unstable Bladder

Excessive caffeine intake (more than 400 mg/day) may increase the risk of detrusor instability (unstable bladder) in women ( 157 ). For women with preexisting bladder symptoms, even moderate caffeine intake (200–400 mg/day) may increase the risk for unstable bladder ( 157 ). This finding was confirmed in another case–control study of women who were given 200 mg of caffeine citrate ( 158 ). In addition, caffeine intake of 4.5 mg/kg/day caused early urgency and frequency of urination in men and women with overactive bladder ( 159 ). However, these studies did not examine whether a decrease in caffeine intake was associated with improvements in overactive bladder symptoms. Studies should address this issue.

Caffeine–Drug Interactions

According to www.drugs.com (a site owned by The Drugsite Trust, a privately held Trust administered by two New Zealand Pharmacists), 85 drugs (430 brand and generic names) are known to interact with caffeine, of which 11 can lead to major interactions. 2 Because caffeine consumption is at an all-time high and prescription drug use is more prevalent than ever, the risk of negative caffeine and prescription drug interactions is increasing ( 160 , 161 ). Because of the popularity of caffeine, clinicians should be conscious of the pharmacokinetic interactions between dietary caffeine and over-the-counter and prescription medications, and they should provide the necessary guidance to the patient including dietary restrictions. We also recommend that the potential interaction with these drugs be appropriately addressed on the labeling.

Hydration and Diuresis

Caffeine has a diuretic effect ( 123 , 162 , 163 ). However, in one clinical trial, different doses of caffeine (up to 6 mg/kg body weight) consumed by 59 habitual caffeine consumers after a 6-day run-in period of 3 mg/kg of caffeine did not markedly change hydration-related biomarkers, suggesting that increasing doses of caffeine did not induce hypohydration in these participants ( 164 ). These findings are supported by two similar studies, one in which 5 mg/kg body weight of caffeine was consumed daily for 4 consecutive days by 30 men who normally consumed less than 100 mg/day ( 42 ) and one in which 4 mg/kg body weight/day of caffeine from coffee was consumed for 3 consecutive days by 50 adult male habitual coffee consumers who usually consumed 3–6 cups of coffee/day ( 165 ). These findings suggest that the diuretic effects from consuming between 4 and 6 mg/kg body weight/day of caffeine are not likely to have adverse consequences for healthy adults who are habitual consumers of caffeine. Similar studies should be conducted in populations that vary by health status, age, and sex.

Populations At-Risk for Harmful Effects of Caffeine

Pregnant and lactating women.

Pregnant women and fetuses may be particularly vulnerable to the effects of caffeine. Caffeine is a biologically active molecule that can act on multiple targets and affect numerous functions positively or negatively. At early stages of fetal development, caffeine may have deleterious effects ( 137 ). A recent prospective study suggests that preconception caffeine consumption may also pose a risk to pregnancy, with pre-pregnancy consumption of >400 mg of caffeine/day increasing the risk of spontaneous abortion by 11% compared with women who consumed <50 mg of caffeine/day ( 131 ). Many psychoactive compounds can cross the placental barrier and alter the development of the fetal brain. Once caffeine enters the fetal circulation, it is metabolized slowly because neither the placenta nor the fetus itself has cytochrome P450, the enzyme that metabolizes caffeine ( 166 ). This reduced caffeine metabolism results in a longer half-life and increased caffeine exposure to the fetus ( 141 , 167 ). The American College of Obstetricians and Gynecologists recommends limiting caffeine consumption during pregnancy to less than 200 mg/day ( 168 ). In the late 1970s, most women maintained their intake during pregnancy at an average of about 190 mg/day 3 ( 5 ). In the 1980s and 1990s, the average maternal caffeine consumption declined to about 125 mg/day ( 5 ). Consumption was reported to be about 123 mg/day between 1997 and 2007 ( 84 , 85 ) and was even lower (58 mg/day) in a 1999 survey ( 169 ). This decline has been attributed to FDA warnings that excess caffeine consumption during pregnancy may adversely affect neonates ( 170 ). Interestingly, however, in a small cohort of 105 women who drank coffee before pregnancy, 65% reported an aversion to coffee during the first trimester, and 95% voluntarily reduced their consumption during this trimester ( 171 ), so perhaps women might be naturally averse to caffeinated products during pregnancy.

Data on caffeine consumption during lactation are limited. One small study from Poland reported that average caffeine intake in a sample of lactating women ranged from 127 to 163 mg/day ( 172 ).

Children and Adolescents

Young children may be vulnerable to the effects of caffeine because they weigh less. For example, a typical can of soda contains about 45 mg of caffeine on average. In an adult weighing 70 kg, the effective dose is 0.6 mg/kg, but in a child weighing 20 kg, the effective dose of the same soda would be 2.25 mg/kg. In comparison, the average caffeine intake in adults is 180 mg/day, resulting in an average effective dose of 2.5 mg/kg. Thus, the physiological impact of a single soda in a child may be equivalent to the impact of two cups of coffee in an average-sized adult. Adolescents may also be particularly vulnerable to the sleep-disrupting effects of caffeine because they may also use caffeinated beverages to stay awake ( 173 , 174 ).

Data have been collected in children and adolescents using dose–response and placebo-controlled research methods. Outcomes, such as cardiovascular function ( 175 – 178 ), mood ( 179 – 181 ), and cognitive performance ( 82 , 182 ), have all been measured at caffeine doses ranging from 50 to 300 mg. None of the results suggest that caffeine at these doses is acutely harmful to children and adolescents ( 183 ).

Some studies suggest an association between caffeine consumption and longer term behavioral problems in youth, such as anger, violence, sleep disturbances, and alcohol and drug use ( 180 , 184 ). Researchers in Iceland surveyed 7,400 adolescents (aged 14 and 15 years) and found that most reported consuming caffeine on a typical day and that caffeine intake (primarily from soda and energy drinks) was related to daytime sleepiness and anger for both sexes ( 185 ). In a 2013 study of 3,747 15- to 16-year olds, self-reported caffeine intake was strongly associated with self-reported violent behavior and conduct disorders ( 186 ). In this study, 21% of participants consumed at least one energy drink per day.

Other studies have found that anxiety can be produced at a wide range of doses (200–2,000 mg of caffeine/day), but many of these studies have used psychiatric patients or patients with a preexisting anxiety disorder ( 123 ). Other effects in these studies included nervousness, fidgeting, jitteriness, restlessness, hyperactivity, and sleeplessness ( 123 , 187 , 188 ). When children were stratified by prestudy caffeine intake, emotions and behaviors differed between low- and high-dose consumers ( 187 , 188 ). Children consuming high doses were more easily frustrated and were more nervous during baseline tests than were the children consuming lower doses. Other studies have found that children with attention-deficit/hyperactivity disorder have higher rates of caffeine abuse, perhaps due to the additive effects of caffeine on dopamine action at the dopamine D2 dopamine receptor, similar to the way guanfacine works for children with this disorder ( 189 , 190 ).

The safety of high-dose caffeine and energy drinks in younger individuals and caffeine-naïve individuals has not yet been determined. The consumption of highly caffeinated energy drinks has been associated with elevated blood pressure, altered heart rates, and severe cardiac events in children, adolescents, and young adults, especially those with underlying cardiovascular diseases ( 115 , 177 , 191 , 192 ). For example, a study of 50 young adults found that consuming a sugar-free energy drink containing 80 mg of caffeine (slightly less than the caffeine contained in one cup of coffee) was associated with changes in platelet and endothelial function great enough to increase the risk for severe cardiac events in susceptible individuals ( 193 ). These findings show how the acute effects of caffeine on heart rate might result in cardiovascular events requiring hospitalization, especially in at-risk young adults. In addition, caffeine’s effects on blood pressure are more pronounced among African-American children than among Caucasian children (mean difference in blood pressure averaging 6.5 mm Hg) ( 175 , 194 ). High doses of caffeine may exacerbate cardiac conditions for which stimulants are contraindicated ( 195 – 198 ). In particular, ion channelopathies and hypertrophic cardiomyopathy, which is the most prevalent genetic cardiomyopathy in children and young adults (0.2% of the population), are of concern because of the risk of hypertension, syncope, arrhythmias, and sudden death ( 197 , 199 ).

Patients with Mental Illness

Another population that may be at risk for adverse effects of caffeine are patients with mental illness. Caffeine antagonism of adenosine receptors can result in enhanced dopaminergic signaling, thought to be due to a combination of increased dopamine release ( 200 , 201 ), upregulation of dopamine receptors, and increased affinity of dopamine receptors for dopamine in the striatum and nucleus accumbens ( 202 ). Furthermore, adenosine receptors can form heterodimers with dopamine receptors ( 203 ), which can modulate dopamine signaling. For some psychiatric illness, such as Parkinson’s disease, Alzheimer’s disease, and depression, caffeine antagonism of adenosine receptors may improve symptoms ( 204 , 205 ) and slow the progression of neurodegeneration ( 206 , 207 ), although these findings are equivocal with some studies reporting caffeine increases depressive symptoms ( 208 ). For other mental illness, such as schizophrenia, caffeine may exacerbate psychotic symptoms ( 209 ), although the majority of this literature is informed by case studies, with very few double-blind placebo-controlled studies ( 210 ). There is also good evidence that higher caffeine use is associated with greater reporting of anxiety symptoms ( 211 , 212 ) and may increase risk of symptom relapse ( 213 ) and suicide among bipolar disorder patients ( 214 ). Finally, there is strong empirical evidence that caffeine potentiates the rewarding effects of drugs of abuse ( 215 – 217 ), which suggests that caffeine use can increase vulnerability to substance use disorder ( 218 ). The lack of randomized control trials on the impact of caffeine in patients with mental illness makes it difficult to determine safe doses, effects of acute and chronic caffeine, and potential interactions between caffeine and medications. Currently, there are no specific recommendations for caffeine consumption for individuals with mental or psychiatric illness, but it may be worth consideration by physicians and psychologists treating patients with mental illness.

Caffeine and Alcohol

Another increasingly popular form of caffeine consumption is to mix alcohol with energy drinks. In fact, there are several recent reviews on this topic ( 219 – 221 ). We will briefly highlight this literature here. In 2010, the FDA removed pre-mixed alcohol-energy drinks from the market because caffeine was determined to be an unsafe additive to alcohol, 4 in part because it promoted excessive drinking ( 222 ). However, energy drinks can be legally mixed with alcohol in the U.S. if they are sold separately. In fact, this practice is popular among college students, as suggested by the increase in self-reports over the past 5–10 years ( 223 – 229 ). The research on alcohol-mixed energy drinks is still developing, and the vast majority has been conducted in the U.S. and Australia. Much of this research consists of surveys of college-age young adults immediately after they leave bars where they have been drinking ( 230 – 233 ). Self-report is often unreliable, but self-report while intoxicated may be particularly problematic. Similarly, intoxication may confound retrospective assessments of alcohol consumption and related behaviors and attitudes.

More recently, several well-controlled, objective, laboratory-based studies on the impact of alcohol-mixed energy drinks have been conducted. In many studies, the combination of alcohol and energy drinks results in higher rates of binge drinking, reductions in perceived intoxication, faster rates of self-paced alcohol consumption, or increases in risk taking behavior ( 225 , 234 – 239 ). These data are equivocal, however, with studies showing that caffeine combined with alcohol does not always increase the amount of alcohol consumed ( 240 ) or does not have an impact on risk taking behavior ( 235 , 241 ). Potential reasons for these discrepancies may be difference in the doses of caffeine and alcohol, differences in the administration paradigm, and an influence of expectancy of caffeine effects on alcohol intoxication ( 241 ). More work is needed in this area to be able to draw stronger conclusions.

Caffeine-Related Diagnoses

The American Psychiatric Association’s Diagnostic and Statistical Manual-IV ( 242 ) included four caffeine-related diagnoses: caffeine intoxication, caffeine-induced anxiety disorder, caffeine-induced sleep disorder, and caffeine-related disorder not otherwise specified ( 242 ). Caffeine intoxication is diagnosed if clinically significant impairment results from the following criteria: (1) recent consumption of caffeine, usually in excess of 250 mg, (2) five (or more) of the following: restlessness, nervousness, excitement, insomnia, flushed face, diuresis, gastrointestinal disturbance, muscle twitching, rambling flow of thought and speech, tachycardia or cardiac arrhythmia, periods of inexhaustibility, psychomotor agitation, and (3) the symptoms in criteria (2) have to cause clinically significant distress or impairment in social, occupational, or other important areas of functioning and these symptoms cannot be attributable to another medical condition or mental disorder. Caffeine-induced anxiety and sleep disorder retain the diagnosis for substance/medication-induced anxiety and sleep disorders, but require that clinically significant symptoms occur in association with caffeine intoxication or withdrawal ( 243 ). Caffeine-related disorder not otherwise specified classifies symptoms related to caffeine use or withdrawal that do not fit into the aforementioned categories.

The latest edition of the DSM ( 243 ) has officially recognized caffeine withdrawal disorder and outlines guidelines for criteria for caffeine use disorder in a section on emerging measures and models ( 243 ). The diagnosis of caffeine withdrawal syndrome is empirically based on detailed analyses of decades of studies of symptoms [reviewed by Juliano and Griffiths ( 244 )]. Caffeine withdrawal disorder is diagnosed when an individual experiences clinically significant impairment related to withdrawal symptoms after abrupt cessation of caffeine intake, including headache, difficulty concentrating, fatigue, nausea, flu-like symptoms, and changes in mood. These symptoms typically begin 12–24 h after caffeine cessation and may continue for 3–7 days. Ongoing research on caffeine withdrawal suggests that this continues to be an important problem and will help refine and clarify this diagnosis ( 245 , 246 ). Avoidance of caffeine withdrawal, with or without a diagnosis of caffeine withdrawal disorder, may motivate individuals to consume more caffeine. This could result in chronic, excessive consumption of caffeine. When this excess consumption results in clinically significant impairment, an individual may meet the criteria for caffeine use disorder ( 247 – 249 ). Although not an official DSM diagnosis, the proposed criteria for caffeine use disorder include having all three of the following criteria met: (1) persistent desire or unsuccessful effort to control caffeine use, (2) “use despite harm,” and (3) withdrawal. Having these proposed criteria outlined will allow researchers to collect data to provide reliable and valid empirical studies of the prevalence of this phenomenon ( 250 ). This is critical because the progression of inclusion of caffeine-related diagnoses is directly related to an increase in empirical support for such disorders.

Recommendations on Safe Intake Levels and Limits on Intake

Caffeine reaches maximum plasma concentration 15–120 min after ingestion ( 251 ), which might explain why energy drink-related adverse events are usually reported a few hours after consumption. The threshold of caffeine toxicity appears to be around 400 mg/day in healthy adults (19 years or older), 100 mg/day in healthy adolescents (12–18 years old), and 2.5 mg/kg/day in healthy children (less than 12 years old) ( 123 , 192 ). For comparison, one standard sized can of a popular energy drink provides 77 mg of caffeine (or 1.1 mg/kg/day) for a 70-kg male and twice that, 2.2 mg/kg/day, for a 35-kg pre-teen ( 252 ). Recommended safety thresholds vary, however. For example, the European Food and Safety Authority considers 3-mg/kg body weight/day of habitual caffeine consumption to be safe for children and adolescents ( 253 ). 5

A comprehensive review of the effects of caffeine consumption on human health concluded that for healthy adults, moderate chronic intakes of caffeine up to 400 mg/day are not associated with adverse effects on cardiovascular health, calcium balance and bone status, behavior, cancer risk, or male fertility ( 123 ). However, the recommended intake is much lower for pregnant or nursing mothers. The European Commission’s Scientific Committee of Food Safety Authority and Health Canada both recommend that women consume no more than 300 mg of caffeine/day during pregnancy ( 121 , 253 ). In addition, despite conflicting results regarding the association between caffeine consumption and spontaneous abortion, the American College of Obstetricians and Gynecologists recommends that pregnant women restrict their caffeine intake to less than 200 mg/day ( 121 ).

For most children, adolescents, and young adults, safe levels of caffeine consumption have not been established. Because deleterious effects of heavy caffeine use have been documented in those who have cardiovascular issues, studies of safe doses and the effects of chronic use are paramount in understanding the implications of caffeine. This research should seek to better characterize the effects of caffeine use before, during, and after exercise, the interactions of caffeine use with alcohol and medications, such as stimulants, and the effects of prolonged caffeine use. A better understanding of caffeine’s effects in individuals with cardiac problems will better equip health-care providers to screen and identify at-risk individuals, and in turn, to better educate and counsel these cardiac patients. Such information will also help health-care leaders to work with families, schools, and other community services to change marketing strategies, improve the dissemination of information, and identify at-risk behaviors and age groups. Finally, the health-care providers and regulatory agencies must begin collecting and archiving better data on the adverse events and health effects of caffeine consumption to improve estimates about its scope, effects, and outcomes. Analyses of a comprehensive, centralized database would help direct research, education, and funding to support these populations. In addition, agencies like the U.S. FDA and Health Canada need to initiate programs to educate consumers, especially children and adolescents, about the dangers of highly caffeinated products, to reconsider applying the U.S. FDA’s Generally Recognized as Safe standard to energy drinks and other beverages with added caffeine, and requiring manufacturers to include the caffeine content on product labels. Because of the potentially harmful adverse effects and developmental effects of caffeine, the consensus among the research and medical communities is that any dietary intake of caffeinated energy drinks should be discouraged for all children ( 123 , 192 ).

One of the primary concerns about energy drinks is that the actual caffeine content is not often given on the product’s packaging or on its website ( 120 ). The total amount of caffeine contained in some energy drinks can exceed 500 mg (equivalent to 14 cans of common caffeinated soft drinks or 5 cups of coffee) and is high enough to be toxic in children and young adults ( 34 ). Given these concerns, the American Academy of Pediatrics released the following recommendation to the United States Senate Committee on Commerce, Science, and Transportation:

Due to the potentially harmful health effects of caffeine, dietary intake should be discouraged for all children. Because the actual stimulant content of energy drinks is hard to determine, energy drinks pose an even greater health risk than simple caffeine. Therefore, energy drinks are not appropriate for children and adolescents and should never be consumed (2014).

In 2010, Health Canada convened an Expert Panel 6 on Caffeinated Energy Drinks to develop a plan to more effectively address the safety concerns related to caffeinated energy drinks currently marketed in Canada. The Panel issued their recommendations to Health Canada in the fall of 2010. 7 Health Canada analyzed the recommendations, completed a health risk assessment, and continued to gather and exchange information with major food safety regulators within the country and internationally. This initiative resulted in a proposed management approach that was consistent with the strategies in the Panel’s recommendations. Components of this approach include regulating product formulation and labeling, addressing potential health risks and adverse effects, providing enhanced education and communication to consumers, and addressing uncertainties and data gaps through research on long-term effects. Long-term research was made a priority, to further investigate risks to consumers, to identify serious adverse event signals (such as cardiac events and to a lesser extent, seizures), and finally to better manage caffeine labeling and dosing limits. The data have reconfirmed that moderate daily caffeine intake at dosages of up to 400 mg/day are not associated with adverse effects. However, the data show that women of childbearing age and children may be at higher risk from caffeine, which has therefore led to separate guidelines for these at-risk groups. However, several products containing stimulant drugs do not have a natural health product license and exemption numbers that clearly describe their caffeine content. Therefore, the Panel recommended that Health Canada ensure that all products meet strict labeling that includes a full disclosure of the exact caffeine dose. Finally, the Panel recommended that Health Canada, in collaboration with the provinces and territories, consider beginning a surveillance system in sentinel emergency rooms across the country to actively search for serious adverse drug reactions associated with consuming drinks containing stimulant drugs with or without alcohol or other products. The proposal details how this system could be modeled after the nation’s long-running IMPACT system that monitors immunizations and related adverse events through a network of 12 Canadian centers, representing 90% of all tertiary care pediatric beds. A similar database, The Canadian Health Measures Survey, 8 launched in 2007, contains data from voluntary household interviews that collects important health information (e.g., physical measurements, nutrition, and blood and urine samples).

Future Research

Several questions remain about caffeine consumption and patterns of intake. First, it is not clear how much caffeine is being consumed from “uncommon” or unidentified sources of caffeine, such as foods and medications. These sources are often overlooked in large national surveys and, thus, caffeine intake may be underestimated. Second, caffeine may be indirectly harmful because it is consumed with other substances that are harmful. For example, coffee drinking may promote donut eating or cigarette smoking, or energy drink consumption may promote alcohol intake. Third, future studies need to investigate absorption, distribution, metabolism, and excretion of caffeine occurring in non-natural forms (such as encapsulated forms), which may influence pharmacokinetics, and thus effects. Finally, most research has relied on self-report and correlational analysis, which limits the ability to determine causality and directionality.

Despite all that is known about caffeine intake and safety of caffeine consumption, certain gaps in our knowledge need to be addressed:

(1) Identifying at-risk populations for caffeine toxicity . We already know that small children and pregnant women, as well as individuals with cardiac or vascular disease, are likely to be particularly vulnerable to the harmful effects of caffeine. Furthermore, there is some evidence that individuals with mental illness may also be at risk for harmful effects of caffeine on symptoms, but the majority of these relationships have been described in case studies. More randomized control trials need to be conducted in patients with mental illness to determine safe doses for caffeine ingestion. In addition to the known vulnerable populations, there may be individuals, such as the elderly or individuals with underlying medical conditions, who are not part of any vulnerable population but who, for genetic or metabolic reasons, may be susceptible to harmful effects. The Federal Substance Abuse and Mental Health Services Administration reported that from 2007 to 2011, the number of emergency room visits involving energy drinks doubled across the U.S., from 10,068 to 20,783. However, for adults aged 40 years and older, emergency room visits involving energy drinks nearly quadrupled during that same period (from 1,382 to 5,233). 9 This finding suggests that energy drink consumption in older people is increasing with perhaps a greater risk of negative outcomes. Identifying and warning at-risk individuals to avoid caffeine-containing products would be desirable.

(2) Determining how best to disseminate information about caffeine content in a meaningful and truthful way without causing alarm . Although the preponderance of evidence suggests that caffeine is safe for most people, there may be reasons to limit caffeine use in some populations. Providing more information about safe levels may be useful, but the information must be understandable to the population and based on evidence, rather than on supposition. Adding information about caffeine content on the products themselves may not be enough. The best way to educate consumers about safe levels of caffeine consumption needs to be determined. For example, evidence suggests that “natural frequencies” are an effective way to communicate risk. For example, one could explain “For every 1,000 children who consume energy drinks, XX will have CNS symptoms.” However, research is necessary to fill in the blank in this statement ( 254 ).

(3) Conducting prospective, longitudinal studies to determine how caffeine use relates to behavioral and health-related outcomes , such as the duration and quality of sleep, potential for abuse, and impact on the use of other substances, including controlled (cigarettes and e-cigarettes) and uncontrolled (marijuana, cocaine) drugs. Cross-sectional data suggest that caffeine use is generally safe, but rigorous longitudinal studies have not yet determined the effect of chronic caffeine consumption on development in children and adolescents.

(4) Further exploring the potential health benefits of caffeine . Although much of this document has focused on potential harmful effects of caffeine, some health benefits of caffeine remain under explored. In particular, some research suggests that caffeine may slow age-related cognitive decline ( 255 , 256 ), reduce risk of some neurological disorders ( 90 , 257 , 258 ), and promote longevity ( 156 ).

(5) Developing better systems of documenting and sharing adverse events . In addition to identifying at-risk or vulnerable populations, as mentioned earlier, and potentially dangerous combinations of caffeine with other substances (e.g., alcohol), we need a better system of documenting adverse events and sharing that documentation among scientists and clinicians. Systematically collecting all adverse events, poison center data, and emergency room visits associated with caffeine consumption (for example, energy drink consumption), together with more comprehensive evaluation of additional risk factors, is necessary to accurately determine the risks of toxicity for youth and other vulnerable individuals.

(6) Improving knowledge of the potential dangers from consuming energy drinks before, during, and after athletic activity will be essential to identify the potential dangers of direct and implied claims of enhanced athletic performance, which is common in energy drink marketing. Long-term systematic assessment of energy drink and general caffeine intake at the population level, specifically intake by youth, should be a priority.

When taken together, the literature reviewed here suggests that ingested caffeine is relatively safe at doses typically found in commercially available foods and beverages. There are some trends in caffeine consumption, such as alcohol-mixed energy drinks, that may increase risk of harm. There are also some populations, such as pregnant women, children, and individuals with mental illness, who may also be considered vulnerable for harmful effects of caffeine. Excess caffeine consumption is increasingly being recognized by health-care professionals and by regulatory agencies as potentially harmful. More research needs to be conducted to address these emerging concerns and provide empirical support for the recommendations.

Author Contributions

JT, CB, and SL contributed equally to the preparation of this comprehensive review. JC, JW, and MM helped gather additional references and prepare the manuscript after the initial major review of the literature was conducted.

Conflict of Interest Statement

The authors prepared this comprehensive review at the request of the American Association for the Advancement of Science. Once the draft was completed, we were given permission to publish the manuscript. SL has served as an expert for legal cases involving caffeine-containing energy drinks.

CB is funded by l’Agence Nationale de la Recherche (ANR, ANR-14-CE13-0032-02 ADONIS), JT is funded by the National Institutes of Health (DA021759, DA030386, and DK106265). SL is funded by the National Institutes of Health (HL111459, HL109090, HL078522, HL053392, HL079233, HL087000, HL095127, HD060325, NR012885, CA127642, CA068484, and HD052104).

• ^ https://www.fda.gov/ForConsumers/ConsumerUpdates/ucm350570.htm .
• ^ https://www.drugbank.ca/drugs/DB00201#pharmacology .
• ^ It is difficult to calculate the caffeine intake relative to body weight during pregnancy because women begin pregnancy at a broad range of weights, gain weight at different rates, and gain different amounts of weight. Because of this, only absolute caffeine intake is shown in this section.
• ^ https://www.fda.gov/NewsEvents/PublicHealthFocus/ucm234900.htm .
• ^ http://www.efsa.europa.eu/en/efsajournal/pub/4102 .
• ^ http://www.hc-sc.gc.ca/dhp-mps/prodnatur/activit/groupe-expert-panel/index-eng.php .
• ^ http://www.hc-sc.gc.ca/fn-an/securit/addit/caf/ced-response-bec-eng.php .
• ^ http://www23.statcan.gc.ca/imdb/p2SV.pl?Function=getSurvey&SDDS=5071 .
• ^ http://www.samhsa.gov/data/sites/default/files/DAWN126/DAWN126/sr126-energy-drinks-use.pdf .

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248. Budney AJ, Lee DC, Juliano LM. Evaluating the validity of caffeine use disorder. Curr Psychiatry Rep (2015) 17:74. doi:10.1007/s11920-015-0611-z

249. Evatt DP, Juliano LM, Griffiths RR. A brief manualized treatment for problematic caffeine use: a randomized control trial. J Consult Clin Psychol (2016) 84:113–21. doi:10.1037/ccp0000064

250. Addicott MA. Caffeine use disorder: a review of the evidence and future implications. Curr Addict Rep (2014) 1:186–92. doi:10.1007/s40429-014-0024-9

251. Arnaud MJ. The pharmacology of caffeine. Prog Drug Res (1987) 31:273–313.

252. Oddy WH, O’Sullivan TA. Energy drinks for children and adolescents. BMJ (2009) 339:b5268. doi:10.1136/bmj.b5268

253. Miles-Chan JL, Charriere N, Grasser EK, Montani JP, Dulloo AG. The blood pressure-elevating effect of red bull energy drink is mimicked by caffeine but through different hemodynamic pathways. Physiol Rep (2015) 3:e12290. doi:10.14814/phy2.12290

254. Gigerenzer G. Reckoning with Risk: Learning to Live with Uncertainty . London: Penguin Books Ltd (2003).

255. Valls-Pedret C, Lamuela-Raventos RM, Medina-Remon A, Quintana M, Corella D, Pinto X, et al. Polyphenol-rich foods in the Mediterranean diet are associated with better cognitive function in elderly subjects at high cardiovascular risk. J Alzheimers Dis (2012) 29:773–82. doi:10.3233/JAD-2012-111799

256. Vercambre MN, Berr C, Ritchie K, Kang JH. Caffeine and cognitive decline in elderly women at high vascular risk. J Alzheimers Dis (2013) 35:413–21. doi:10.3233/JAD-122371

257. Agim ZS, Cannon JR. Dietary factors in the etiology of Parkinson’s disease. Biomed Res Int (2015) 2015:672838. doi:10.1155/2015/672838

258. Nehlig A. Effects of coffee/caffeine on brain health and disease: what should I tell my patients? Pract Neurol (2016) 16:89–95. doi:10.1136/practneurol-2015-001162

Keywords: caffeine, energy drinks, pregnancy, children, adolescence

Citation: Temple JL, Bernard C, Lipshultz SE, Czachor JD, Westphal JA and Mestre MA (2017) The Safety of Ingested Caffeine: A Comprehensive Review. Front. Psychiatry 8:80. doi: 10.3389/fpsyt.2017.00080

Received: 30 January 2017; Accepted: 24 April 2017; Published: 26 May 2017

Reviewed by:

Copyright: © 2017 Temple, Bernard, Lipshultz, Czachor, Westphal and Mestre. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Jennifer L. Temple, jltemple@buffalo.edu

† These authors have contributed equally to this work.

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Caffeine: How much is too much?

Caffeine has its perks, but it can pose problems too. Find out how much is too much and if you need to curb your consumption.

If you rely on caffeine to wake you up and keep you going, you aren't alone. Millions of people rely on caffeine every day to stay alert and improve concentration.

How much is too much?

Up to 400 milligrams (mg) of caffeine a day appears to be safe for most healthy adults. That's roughly the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two "energy shot" drinks. Keep in mind that the actual caffeine content in beverages varies widely, especially among energy drinks.

Caffeine in powder or liquid form can provide toxic levels of caffeine, the U.S. Food and Drug Administration has cautioned. Just one teaspoon of powdered caffeine is equivalent to about 28 cups of coffee. Such high levels of caffeine can cause serious health problems and possibly death.

Although caffeine use may be safe for adults, it's not a good idea for children. Adolescents and young adults need to be cautioned about excessive caffeine intake and mixing caffeine with alcohol and other drugs.

Women who are pregnant or who are trying to become pregnant and those who are breast-feeding should talk with their doctors about limiting caffeine use to less than 200 mg daily.

Even among adults, heavy caffeine use can cause unpleasant side effects. And caffeine may not be a good choice for people who are highly sensitive to its effects or who take certain medications.

Read on to see if you may need to curb your caffeine routine.

You drink more than 4 cups of coffee a day

You may want to cut back if you're drinking more than 4 cups of caffeinated coffee a day (or the equivalent) and you have side effects such as:

• Nervousness
• Irritability
• Frequent urination or inability to control urination
• Fast heartbeat
• Muscle tremors

Even a little makes you jittery

Some people are more sensitive to caffeine than are others. If you're susceptible to the effects of caffeine, even small amounts may prompt unwanted effects, such as restlessness and sleep problems.

How you react to caffeine may be determined in part by how much caffeine you're used to drinking. People who don't regularly drink caffeine tend to be more sensitive to its effects.

You're not getting enough sleep

Caffeine, even in the afternoon, can interfere with your sleep. Even small amounts of sleep loss can add up and disturb your daytime alertness and performance.

Using caffeine to mask sleep deprivation can create an unwelcome cycle. For example, you may drink caffeinated beverages because you have trouble staying awake during the day. But the caffeine keeps you from falling asleep at night, shortening the length of time you sleep.

You're taking medications or supplements

Some medications and herbal supplements may interact with caffeine. Examples include:

• Ephedrine. Mixing caffeine with this medication — which is used in decongestants — might increase your risk of high blood pressure, heart attack, stroke or seizure.
• Theophylline. This medication, used to open up bronchial airways, tends to have some caffeine-like effects. So taking it with caffeine might increase the adverse effects of caffeine, such as nausea and heart palpitations.
• Echinacea. This herbal supplement, which is sometimes used to prevent colds or other infections, may increase the concentration of caffeine in your blood and may increase caffeine's unpleasant effects.

Talk to your doctor or pharmacist about whether caffeine might affect your medications.

Curbing your caffeine habit

Whether it's for one of the reasons above or because you want to trim your spending on coffee drinks, cutting back on caffeine can be challenging. An abrupt decrease in caffeine may cause withdrawal symptoms, such as headaches, fatigue, irritability and difficulty focusing on tasks. Fortunately, these symptoms are usually mild and get better after a few days.

To change your caffeine habit, try these tips:

• Keep tabs. Start paying attention to how much caffeine you're getting from foods and beverages, including energy drinks. Read labels carefully. But remember that your estimate may be a little low because some foods or drinks that contain caffeine don't list it.
• Cut back gradually. For example, drink one fewer can of soda or drink a smaller cup of coffee each day. Or avoid drinking caffeinated beverages late in the day. This will help your body get used to the lower levels of caffeine and lessen potential withdrawal effects.
• Go decaf. Most decaffeinated beverages look and taste much the same as their caffeinated counterparts.
• Shorten the brew time or go herbal. When making tea, brew it for less time. This cuts down on its caffeine content. Or choose herbal teas that don't have caffeine.
• Check the bottle. Some over-the-counter pain relievers contain caffeine. Look for caffeine-free pain relievers instead.

The bottom line

If you're like most adults, caffeine is a part of your daily routine. Usually, it won't pose a health problem. But be mindful of caffeine's possible side effects and be ready to cut back if necessary.

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• Lieberman HR, et al. Daily patterns of caffeine intake and the association of intake with multiple sociodemographic and lifestyle factors in U.S. adults based on the NHANES 2007-2012 surveys. Journal of the American Academy of Nutrition and Dietetics. 2019; doi:10.1016/j.jand.2018.08.152.
• 2015-2020 Dietary Guidelines for Americans. U.S. Department of Health and Human Services and U.S. Department of Agriculture. https://health.gov/our-work/food-nutrition/2015-2020-dietary-guidelines/guidelines. Accessed Feb. 1, 2020.
• Spilling the beans: How much caffeine is too much. U.S. Food and Drug Administration. https://www.fda.gov/consumers/consumer-updates/spilling-beans-how-much-caffeine-too-much. Accessed Sept. 20, 2019.
• Duyff RL. Think your drinks. In: Academy of Nutrition and Dietetics Complete Food and Nutrition Guide. 5th ed. Houghton Mifflin Harcourt; 2017.
• Bordeaux B. Benefits and risks of caffeine and caffeinated beverages. https://www.uptodate.com/contents/search. Accessed Sept. 20, 2019.
• Pure and highly concentrated caffeine. U.S. Food and Drug Administration. https://www.fda.gov/food/dietary-supplement-products-ingredients/pure-and-highly-concentrated-caffeine. Accessed Sept. 20, 2019.
• Caffeine. Natural Medicines. https://naturalmedicines.therapeuticresearch.com. Accessed Feb. 7, 2020.

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NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health.

StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.

StatPearls [Internet].

Justin Evans ; John R. Richards ; Amanda S. Battisti .

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Last Update: May 29, 2024 .

• Continuing Education Activity

Caffeine is a naturally occurring central nervous system stimulant belonging to the methylxanthine class and is widely recognized as the most utilized psychoactive stimulant worldwide. Although this drug is most commonly sourced from coffee beans, it can also naturally occur in certain types of tea and cacao beans and as an additive to soda and energy drinks. Caffeine consumption primarily alleviates fatigue and drowsiness but has numerous additional therapeutic applications. The US Food and Drug Administration (FDA) has approved caffeine for treating apnea of prematurity. Off-label uses of caffeine include the treatment of migraines and post-dural puncture headaches, as well as enhancing athletic performance, particularly in endurance sports.

This activity centers on the mechanism of action, adverse event profile, toxicity, dosing, and monitoring of caffeine, empowering clinicians to identify potential adverse reactions, make informed prescribing decisions, and mitigate risks effectively. This activity underscores how the interprofessional healthcare team's comprehensive knowledge of caffeine's indicated and off-label uses contributes to enhanced patient outcomes.

• Identify appropriate indications for caffeine therapy in clinical practice, including but not limited to apnea of prematurity, migraines, and post-dural puncture headaches.
• Implement evidence-based strategies for dosing caffeine, considering individual patient characteristics and therapeutic goals.
• Apply knowledge of caffeine's mechanism of action and pharmacokinetics to make informed prescribing decisions and monitor treatment efficacy.
• Collaborate with interprofessional healthcare team members to ensure comprehensive patient care, particularly in populations with unique caffeine-related considerations, such as pregnant women and infants.
• Indications

Caffeine is a naturally occurring central nervous system (CNS) stimulant belonging to the methylxanthine class and is widely recognized as the most utilized psychoactive stimulant worldwide. Although this drug is most commonly sourced from coffee beans, it can also naturally occur in certain types of tea and cacao beans. Moreover, the stimulant is also an additive to soda and energy drinks. Caffeine consumption primarily alleviates fatigue and drowsiness but has numerous additional therapeutic applications.

FDA-Approved Indications

The US Food and Drug Administration (FDA) has approved oral caffeine for restoring mental alertness or wakefulness in fatigue or drowsiness.   The FDA has also approved intravenous (IV) caffeine for use in the treatment of apnea of prematurity. [1] [2] [3]  Recommendations from The Association for Professionals in Infection Control and Epidemiology, the Society for Healthcare Epidemiology, the Infectious Diseases Society of America, the American Hospital Association, and The Joint Commission Consensus endorse the use of caffeine within 72 hours after childbirth to aid extubation for the treatment of apnea of prematurity. [4]

Off-Label Uses

IV caffeine is also used for the prevention and treatment of bronchopulmonary dysplasia in premature infants, which often coexists with apnea of prematurity. [5] [6]  Off-label uses of caffeine include the treatment of migraines and post-dural puncture headaches, as well as enhancing athletic performance, particularly in endurance sports. [7] [8] [9]  Caffeine is associated with decreased all-cause mortality. [10] [11]  Moreover, ongoing investigations are exploring its potential efficacy in treating depression and neurocognitive declines, including those observed in Alzheimer and Parkinson diseases. [12] [13] [14]  

According to the American Academy of Family Physicians (AAFP), the combination of acetaminophen, aspirin, and caffeine demonstrates strong evidence of effectiveness in treating acute migraines. [15]  Additionally, acute consumption of caffeine capsules significantly improves muscle strength and endurance, particularly in men. Recent meta-analyses indicate that ingesting caffeine 45 minutes before exercise improves muscle strength and endurance in men. [16]

• Mechanism of Action

Caffeine's primary mechanism of action involves its effects on adenosine receptors in the brain. Being both fat- and water-soluble component, caffeine easily crosses the blood-brain barrier and antagonizes all 4 adenosine receptor subtypes (A1, A2a, A2b, and A3). The antagonism of the A2a receptor is particularly responsible for caffeine's wakefulness effects. [17] [18]

Adenosine receptors are not limited to the CNS but are present throughout the body. Direct antagonism of receptor A1 in cardiac muscles results in positive inotropic effects. Likewise, adenosine receptor antagonism stimulates the release of catecholamines, contributing to the systemic stimulatory effects of caffeine and further stimulating cardiac inotropy and chronotropy. At the vascular level, caffeine undergoes complex interactions to control vascular tone, including direct antagonism of vascular adenosine receptors to promote vasodilation and stimulate endothelial cells to release nitric oxide, which further relaxes vascular smooth muscle cells.

This vasodilation is counteracted by increased sympathetic tone via catecholamine release and positive cardiac inotropic and chronotropic effects, promoting vasoconstriction. Multiple mechanisms of constriction and dilation are at work, resulting in an individualized response dependent on caffeine dose, frequency of use, and comorbidities such as diabetes or hypertension. With infrequent use, caffeine appears to increase systolic blood pressure by approximately 5 to 10 mm Hg. However, little to no acute effect is observed in habitual consumers. [19]

Furthermore, blocking adenosine receptors stimulates respiratory drive by increasing the medullary ventilatory response to carbon dioxide, enhancing central respiratory drive, and improving diaphragm contractility. Caffeine increases renal blood flow, glomerular filtration, and sodium excretion, resulting in diuresis. Additionally, caffeine is a potent stimulator of gastric acid secretion and gastrointestinal motility. [18] [20]

Pharmacokinetics

Absorption: Caffeine has nearly 100% oral bioavailability and is the primary route of administration. In preterm neonates, the average time to achieve peak concentration (Tmax) after oral administration varies between 30 minutes and 2 hours.

Distribution:  Caffeine is rapidly distributed to the brain. The average volume of caffeine distribution in infants (0.8-0.9 L/kg) is slightly higher than in adults (0.6 L/kg). In adults, approximately 36% of caffeine is bound to plasma proteins. [21]

Metabolism:  Caffeine is primarily metabolized in the liver via the cytochrome P450 oxidase system, specifically the enzyme CYP1A2. This metabolism results in 1 of 3 dimethylxanthines, including paraxanthine, theobromine, and theophylline, each with unique effects on the body. These metabolites are then further metabolized and excreted in the urine. [19] [22] [23]

Excretion: Although the half-life of caffeine in the average adult is approximately 5 hours, multiple factors can influence the metabolism and duration. In smokers, the half-life is reduced by up to 50% compared to nonsmokers. Conversely, pregnant patients, especially in the final trimester, may experience a prolonged half-life of up to 15 hours. Newborns also have significantly prolonged half-lives—up to 8 hours for full-term infants and 100 hours for premature infants—due to reduced activity of cytochrome P450 enzymes and immature demethylation pathways. Children older than 9 months have similar half-life eliminations to adults. Additionally, patients with liver disease or those taking cytochrome inhibitors will experience prolonged half-lives due to reduced enzyme activity. [24] [25]

• Administration

Available Dosage Forms and Strengths

Caffeine is obtainable from various sources, including coffee beans, cacao beans, kola nuts, tea leaves, yerba mate, and the guarana berry. In addition, caffeine is commonly found as an additive in sodas and energy drinks or consumed in powder or tablet form. [7]  Absorption may be slightly delayed when taken with food. The stimulant can be administered via the parenteral route, which is a standard method when treating apnea of prematurity in newborns or post-dural puncture headaches. IV formulations are available in 60 mg/3 mL caffeine citrate vials, providing an equivalent dosage of 10 mg/mL caffeine.

Alternatively, caffeine can be absorbed rectally, insufflated, or inhaled. However, consumption through insufflation or inhalation is typically considered a form of misuse aimed at achieving a "high." These routes result in much faster absorption, typically within minutes, and bypass the first-pass metabolism. Although this route can lead to a faster onset of action, multiple studies have demonstrated lower bioavailability from inhaling caffeine, approximately 60% to 70%. Consequently, when taken via these routes, the duration of action is shorter. [22] [26]

Specific Patient Populations

Hepatic impairment:  Caffeine's product labeling does not specify dosage adjustments for individuals with hepatic impairment. However, individuals with advanced cirrhosis may experience delayed caffeine metabolism, leading to adverse drug reactions such as insomnia, nervousness, and headaches, even at intake levels that are typically well tolerated by individuals without liver disease. While caffeine may offer modest protective effects against the progression of chronic liver disease, energy drinks containing harmful supplements may contribute to liver injury. [27]

Renal impairment:  Product labeling does not specify dosage adjustments for renal impairment. Although exposure to caffeine is associated with decreased rates of acute kidney injury during the acute phase in premature neonates, this effect is not observed in term neonates. However, the impact of caffeine exposure on the severity of acute kidney injury, length of hospital stay, morbidity, or mortality remains uncertain. The optimal caffeine dosage for renal protection in neonates has yet to be determined. [28]

Pregnancy considerations:  Caffeine readily crosses the placenta. The American College of Obstetricians and Gynecologists (ACOG) considers 200 mg caffeine daily safe during pregnancy, and no evidence suggests an increased risk of congenital malformations. [29]  However, some studies have suggested that high caffeine consumption during pregnancy (more than 400 mg/d) may be associated with lower birth weights due to intrauterine growth restriction and an increased risk of miscarriage, although not preterm birth. [30] [31]  Nonetheless, the evidence regarding lower birth weight and miscarriage is currently inconclusive and requires further investigation. [32]  Caffeine is considered a pregnancy category C drug. [33]

Breastfeeding considerations:  Caffeine is detectable in breast milk. Infants of mothers with very high caffeine intake, roughly equivalent to consuming 10 or more cups of coffee daily, may experience jitteriness and disrupted sleep patterns. Notably, mothers are suggested to limit their caffeine intake to 300 to 500 mg daily, although European guidelines recommend a likely safe level of 200 mg. Lower intake levels are advisable for mothers of preterm infants due to slower caffeine metabolism in these infants. Additionally, consuming more than 450 mL of coffee daily may decrease iron levels in breast milk, potentially leading to mild iron deficiency anemia in some breastfed infants. [34]

Pediatric patients:  Caffeine citrate injection is FDA-approved for treating apnea of prematurity. According to the manufacturing label, the recommended dosages for this condition are outlined in the table below.

Table. Caffeine Citrate Dosages for Apnea of Prematurity.

Older patients:  According to a cohort study, coffee and caffeine consumption exhibited a notable correlation with a reduced risk of dementia in a dose-dependent manner, especially among men. [35]

• Adverse Effects

As with many drugs or medications, a wide array of adverse effects is associated with caffeine use. These effects vary from mild to severe and, in some cases, can be fatal, depending on the dose consumed and an individual's sensitivity to the drug. The most frequently reported adverse effects are outlined below. Mortality is usually associated with cardiac arrhythmia, hypotension, myocardial infarction, electrolyte disturbances, and aspiration. [11] [36]

Mild Adverse Effects

Mild adverse effects of caffeine include anxiety, restlessness, fidgeting, insomnia, facial flushing, increased urination, irritability, muscle twitches or tremors, agitation, tachycardia or irregular heart rate, and gastrointestinal irritation.

Severe Adverse Effects

Severe adverse effects may include disorientation, hallucinations, psychosis, seizures, arrhythmias, ischemia, and rhabdomyolysis. Additionally, caffeine can lead to withdrawal symptoms if habitual users abruptly cease consumption. These symptoms typically begin 12 to 24 hours after the last intake, peak in 1 to 2 days, and may endure for up to 1 week. However, withdrawal can be avoided by gradually tapering off caffeine rather than abruptly discontinuing it. In the event of symptoms, they can be promptly reversed by re-administering caffeine. [37]

Lastly, when caffeine is used to treat apnea of prematurity, it is normal to observe evidence of an increased risk of necrotizing enterocolitis in neonates. [38]  According to the 2023 guidelines from the American College of Cardiology (ACC), American Heart Association (AHA), American College of Clinical Pharmacy (ACCP), and Heart Rhythm Society (HRS), advising patients with atrial fibrillation to abstain from caffeine to prevent atrial fibrillation episodes lacks supporting evidence. However, caffeine avoidance may alleviate symptoms in patients who find that caffeine exacerbates their atrial fibrillation symptoms.

Current research does not preclude the possibility of individual-specific idiosyncratic reactions between caffeine and atrial fibrillation. Additionally, caffeine may mimic symptoms such as palpitations or enhance awareness of heart rhythm irregularities. [39]  A systematic study supports sleep hygiene recommendations to avoid substantial caffeine intake at least 6 hours before bedtime due to its significant disruptive effects on sleep. [40]

Drug-Drug Interactions

The CYP1A2 enzyme metabolizes caffeine and functions as a competitive inhibitor of this enzyme. Consequently, caffeine can interact with various psychiatric medications, including antidepressants, antipsychotics, anxiolytics, and sedatives. [41]  As CYP1A2 metabolizes tizanidine, concurrent use with caffeine should be avoided. [42]  Additionally, bupropion can lower the seizure threshold, so caution should be exercised when using it concurrently with caffeine. [43]  Furthermore, the sedative effects of alcohol and the psychoactive stimulant effects of caffeine can mask their respective influences on both sleep quantity and sleep quality. [44]

• Contraindications

Although no absolute contraindications to caffeine are recognized, caution is necessary in certain medical conditions, including:

• Documented hypersensitivity
• Severe anxiety
• Cardiovascular disease or symptomatic cardiac arrhythmias
• Peptic ulcer disease or gastroesophageal reflux disease
• Hepatic impairment
• Renal impairment
• Seizures (as caffeine may lower seizure threshold)
• Pregnancy  [45] [46] [47] [48]

The average dose of caffeine for adults is 2.4 mg/kg/d; however, daily doses of up to 400 mg are considered safe. [49]  A 100 mg dose of caffeine generally increases blood levels by 5 to 6 mg/L. [50]  Severe intoxication, characterized by altered mentation, vomiting, and hypotension, has been reported at levels of 80 mg/L. The average blood level in patients who succumb to caffeine toxicity is 180 mg/L (±97 mg/L). [51]  For the treatment of apnea of prematurity, caffeine is administered with therapeutic index goals of 5 to 25 mg/L. [52] [53]

Signs and Symptoms of Overdose

Caffeine consumption is generally regarded as safe. Additive caffeine in most substances does not necessitate FDA approval as long as consumption remains within safe levels stipulated by the statute. A typical dose of caffeine is around 70 to 100 mg per drink. While there is no recommended daily allowance for caffeine, doses of up to 400 mg/d are deemed safe. [54]

The exact LD50 for humans varies and largely depends on individual sensitivity to caffeine. However, the estimated LD50 is between 150 and 200 mg/kg. Case reports indicate that doses as low as 57 mg/kg have resulted in fatalities. A toxic dose of caffeine, where significant adverse effects such as tachycardia, arrhythmia, altered mentation, and seizures may occur, is estimated to be around 1.2 g. The estimates of a life-threatening dose of caffeine range from 10 to 14 g.

Management of Overdose

The treatment for mild ingestions primarily involves supportive care. However, in cases of more severe ingestions, additional interventions may be necessary. Patients may require intubation to protect the airway from vomiting or altered mental status. Benzodiazepines can be administered to abort any seizures that develop. If IV fluid resuscitation fails to address persistent hypotension, patients may need vasopressors. Phenylephrine or norepinephrine is typically the first-line vasopressor, with phenylephrine being preferable due to its α-agonism and reflex bradycardia.

Magnesium and β-blockers can combat cardiac arrhythmias secondary to the hyperadrenergic response. [55]  The ultra-short-acting β1-selective blocker esmolol has been used successfully in several case reports for this indication. In the case of lethal arrhythmias, patients will require defibrillation and resuscitation according to advanced cardiac life support protocols. [45]  Additionally, activated charcoal, intralipid infusion, and hemodialysis can aid in preventing further metabolism and subsequent effects of caffeine overdose. [36] [56]

• Enhancing Healthcare Team Outcomes

Caffeine consumption is generally considered safe in moderate amounts. However, the prevalence of high-energy drinks containing excessive caffeine levels has escalated the problem of caffeine toxicity. [57] These concentrated caffeinated beverages pose a significant risk on their own, but the danger escalates when combined with other illicit substances such as tobacco and alcohol. In recent years, numerous fatalities have been reported following the ingestion of such combinations.

Addressing caffeine toxicity or adverse effects necessitates the collaboration of an interprofessional healthcare team to achieve optimal outcomes. In cases where caffeine is used for apnea of prematurity, consultation with a pediatrician and admission to a neonatal intensive care unit may be necessary. [1]  When using caffeine therapeutically, it is essential to inquire about other potential sources of caffeine to prevent toxicity. Healthcare team members are well-positioned to educate the public about the risks associated with high-energy drinks and related products. Clinicians, nursing staff, and pharmacists should be ready to offer counseling to patients who may be consuming excessive amounts of caffeine. While no absolute contraindications to caffeine exist, patients with cardiac disorders, panic disorder, anxiety, or elevated stress levels should be advised to avoid caffeine. An interprofessional healthcare team is well-equipped to educate patients appropriately in this regard.

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Disclosure: Justin Evans declares no relevant financial relationships with ineligible companies.

Disclosure: John Richards declares no relevant financial relationships with ineligible companies.

Disclosure: Amanda Battisti declares no relevant financial relationships with ineligible companies.

This book is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) ( http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits others to distribute the work, provided that the article is not altered or used commercially. You are not required to obtain permission to distribute this article, provided that you credit the author and journal.

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• Just "Like Coffee" or Neuroenhancement by Stimulants? [Front Public Health. 2021] Just "Like Coffee" or Neuroenhancement by Stimulants? Franke AG, Koller G, Krause D, Proebstl L, Kamp F, Pogarell O, Jebrini T, Manz K, Chrobok AI, Soyka M. Front Public Health. 2021; 9:640154. Epub 2021 Jun 7.
• Review Caffeine and Its Antioxidant Properties-It Is All about Dose and Source. [Int J Mol Sci. 2022] Review Caffeine and Its Antioxidant Properties-It Is All about Dose and Source. Ősz BE, Jîtcă G, Ștefănescu RE, Pușcaș A, Tero-Vescan A, Vari CE. Int J Mol Sci. 2022 Oct 28; 23(21). Epub 2022 Oct 28.
• Review Methylxanthine composition and consumption patterns of cocoa and chocolate products. [Prog Clin Biol Res. 1984] Review Methylxanthine composition and consumption patterns of cocoa and chocolate products. Shively CA, Tarka SM Jr. Prog Clin Biol Res. 1984; 158:149-78.
• Beliefs, Behaviors, and Contexts of Adolescent Caffeine Use: A Focus Group Study. [Subst Use Misuse. 2017] Beliefs, Behaviors, and Contexts of Adolescent Caffeine Use: A Focus Group Study. Ludden AB, O'Brien EM, Pasch KE. Subst Use Misuse. 2017 Jul 29; 52(9):1207-1218. Epub 2017 Jun 12.

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Many of us can’t imagine starting the day without a cup of coffee. One reason may be that it supplies us with a jolt of caffeine, a mild stimulant to the central nervous system that quickly boosts our alertness and energy levels. [1] Of course, coffee is not the only caffeine-containing beverage. Read on to learn more about sources of caffeine, and a review of the research on this stimulant and health.

Absorption and Metabolism of Caffeine

The chemical name for the bitter white powder known as caffeine is 1,3,7 trimethylxanthine. Caffeine is absorbed within about 45 minutes after consuming, and peaks in the blood anywhere from 15 minutes to 2 hours. [2] Caffeine in beverages such as coffee, tea, and soda is quickly absorbed in the gut and dissolves in both the body’s water and fat molecules. It is able to cross into the brain. Food or food components, such as fibers, in the gut can delay how quickly caffeine in the blood peaks. Therefore, drinking your morning coffee on an empty stomach might give you a quicker energy boost than if you drank it while eating breakfast.

Caffeine is broken down mainly in the liver. It can remain in the blood anywhere from 1.5 to 9.5 hours, depending on various factors. [2] Smoking speeds up the breakdown of caffeine, whereas pregnancy and oral contraceptives can slow the breakdown. During the third trimester of pregnancy, caffeine can remain in the body for up to 15 hours. [3]

People often develop a “caffeine tolerance” when taken regularly, which can reduce its stimulant effects unless a higher amount is consumed. When suddenly stopping all caffeine, withdrawal symptoms often follow such as irritability, headache, agitation, depressed mood, and fatigue. The symptoms are strongest within a few days after stopping caffeine, but tend to subside after about one week. [3] Tapering  the amount gradually may help to reduce side effects.

Sources of Caffeine

Caffeine is naturally found in the fruit, leaves, and beans of coffee , cacao, and guarana plants. It is also added to beverages and supplements. There is a risk of drinking excess amounts of caffeinated beverages like soda and energy drinks because they are taken chilled and are easy to digest quickly in large quantities.

• Coffee. 1 cup or 8 ounces of brewed coffee contains about 95 mg caffeine. The same amount of instant coffee contains about 60 mg caffeine. Decaffeinated coffee contains about 4 mg of caffeine. Learn more about coffee .
• Espresso. 1 shot or 1.5 ounces contains about 65 mg caffeine.
• Tea. 1 cup of black tea contains about 47 mg caffeine. Green tea contains about 28 mg. Decaffeinated tea contains 2 mg, and herbal tea contains none. Learn more about tea .
• Soda. A 12-ounce can of regular or diet dark cola contains about 40 mg caffeine. The same amount of Mountain Dew contains 55 mg caffeine.
• Chocolate (cacao) . 1 ounce of dark chocolate contains about 24 mg caffeine, whereas milk chocolate contains one-quarter of that amount.
• Guarana. This is a seed from a South American plant that is processed as an extract in foods, energy drinks, and energy supplements. Guarana seeds contain about four times the amount of caffeine as that found in coffee beans. [4] Some drinks containing extracts of these seeds can contain up to 125 mg caffeine per serving.
• Energy drinks. 1 cup or 8 ounces of an energy drink contains about 85 mg caffeine. However the standard energy drink serving is 16 ounces, which doubles the caffeine to 170 mg. Energy shots are much more concentrated than the drinks; a small 2 ounce shot contains about 200 mg caffeine. Learn more about energy drinks .
• Supplements. Caffeine supplements contain about 200 mg per tablet, or the amount in 2 cups of brewed coffee.

Recommended Amounts

In the U.S., adults consume an average of 135 mg of caffeine daily, or the amount in 1.5 cups of coffee (1 cup = 8 ounces). [5] The U.S. Food and Drug Administration considers 400 milligrams (about 4 cups brewed coffee) a safe amount of caffeine for healthy adults to consume daily. However, pregnant women should limit their caffeine intake to 200 mg a day (about 2 cups brewed coffee), according to the American College of Obstetricians and Gynecologists.

The American Academy of Pediatrics suggests that children under age 12 should not consume any food or beverages with caffeine. For adolescents 12 and older, caffeine intake should be limited to no more than 100 mg daily. This is the amount in two or three 12-ounce cans of cola soda.

Caffeine and Health

Caffeine is associated with several health conditions. People have different tolerances and responses to caffeine, partly due to genetic differences. Consuming caffeine regularly, such as drinking a cup of coffee every day, can promote caffeine tolerance in some people so that the side effects from caffeine may decrease over time. Although we tend to associate caffeine most often with coffee or tea, the research below focuses mainly on the health effects of caffeine itself. Visit our features on coffee , tea , and energy drinks for more health information related to those beverages.

Caffeine can block the effects of the hormone adenosine, which is responsible for deep sleep . Caffeine binds to adenosine receptors in the brain, which not only lowers adenosine levels but also increases or decreases other hormones that affect sleep, including dopamine, serotonin, norepinephrine, and GABA. [2] Levels of melatonin, another hormone promoting sleep, can drop in the presence of caffeine as both are metabolized in the liver. Caffeine intake later in the day close to bedtime can interfere with good sleep quality. Although developing a caffeine tolerance by taking caffeine regularly over time may lower its disruptive effects, [1] those who have trouble sleeping may consider minimizing caffeine intake later in the day and before going to bed.

In sensitive individuals, caffeine can increase anxiety at doses of 400 mg or more a day (about 4 cups of brewed coffee). High amounts of caffeine may cause nervousness and speed up heart rate, symptoms that are also felt during an anxiety attack. Those who have an underlying anxiety or panic disorder are especially at risk of overstimulation when overloading on caffeine.

Caffeine stimulates the heart, increases blood flow, and increases blood pressure temporarily, particularly in people who do not usually consume caffeine. However, strong negative effects of caffeine on blood pressure have not been found in clinical trials, even in people with hypertension, and cohort studies have not found that coffee drinking is associated with a higher risk of hypertension. Studies also do not show an association of caffeine intake and atrial fibrillation (abnormal heart beat), heart disease , or stroke. [3]

Caffeine is often added to weight loss supplements to help “burn calories.” There is no evidence that caffeine causes significant weight loss. It may help to boost energy if one is feeling fatigued from restricting caloric intake, and may reduce appetite temporarily. Caffeine stimulates the sympathetic nervous system, which plays a role in suppressing hunger, enhancing satiety, and increasing the breakdown of fat cells to be used for energy. [6] Cohort studies following large groups of people suggest that a higher caffeine intake is associated with slightly lower rates of weight gain in the long term. [3] However, a fairly large amount of caffeine (equivalent to 6 cups of coffee a day) may be needed to achieve a modest increase in calorie “burn.” Additional calories obtained from cream, milk, or sweetener added to a caffeinated beverage like coffee or tea can easily negate any calorie deficit caused by caffeine.

Caffeine can cross the placenta, and both mother and fetus metabolize caffeine slowly. A high intake of caffeine by the mother can lead to prolonged high caffeine blood levels in the fetus. Reduced blood flow and oxygen levels may result, increasing the risk of miscarriage and low birth weight. [3] However, lower intakes of caffeine have not been found harmful during pregnancy when limiting intakes to no more than 200 mg a day. A review of controlled clinical studies found that caffeine intake, whether low, medium, or high doses, did not appear to increase the risk of infertility. [7]

Most studies on liver disease and caffeine have specifically examined coffee intake. Caffeinated coffee intake is associated with a lower risk of liver cancer, fibrosis, and cirrhosis. Caffeine may prevent the fibrosis (scarring) of liver tissue by blocking adenosine, which is responsible for the production of collagen that is used to build scar tissue. [3]

Studies have shown that higher coffee consumption is associated with a lower risk of gallstones. [8] Decaffeinated coffee does not show as strong a connection as caffeinated coffee. Therefore, it is likely that caffeine contributes significantly to this protective effect. The gallbladder is an organ that produces bile to help break down fats; consuming a very high fat diet requires more bile, which can strain the gallbladder and increase the risk of gallstones. It is believed that caffeine may help to stimulate contractions in the gallbladder and increase the secretion of cholecystokinin, a hormone that speeds the digestion of fats.

Caffeine may protect against Parkinson’s disease. Animal studies show a protective effect of caffeine from deterioration in the brain. [3] Prospective cohort studies show a strong association of people with higher caffeine intakes and a lower risk of developing Parkinson’s disease. [9]

Caffeine has a similar action to the medication theophylline, which is sometimes prescribed to treat asthma. They both relax the smooth muscles of the lungs and open up bronchial tubes, which can improve breathing. The optimal amount of caffeine needs more study, but the trials reviewed revealed that even a lower caffeine dose of 5 mg/kg of body weight showed benefit over a placebo. [10] Caffeine has also been used to treat breathing difficulties in premature infants. [3]

Caffeine stimulates the release of a stress hormone called epinephrine, which causes liver and muscle tissue to release its stored glucose into the bloodstream, temporarily raising blood glucose levels. However, regular caffeine intake is not associated with an increased risk of diabetes . In fact, cohort studies show that regular coffee intake is associated with a lower risk of type 2 diabetes , though the effect may be from the coffee plant compounds rather than caffeine itself, as decaffeinated coffee shows a similar protective effect. [3] Other observational studies suggest that caffeine may protect and preserve the function of beta cells in the pancreas, which are responsible for secreting insulin. [11]

Signs of Toxicity

Caffeine toxicity has been observed with intakes of 1.2 grams or more in one dose. Consuming 10-14 grams at one time is believed to be fatal. Caffeine intake up to 10 grams has caused convulsions and vomiting, but recovery is possible in about 6 hours. Side effects at lower doses of 1 gram include restlessness, irritability, nervousness, vomiting, rapid heart rate, and tremors.

Toxicity is generally not seen when drinking caffeinated beverages because a very large amount would need to be taken within a few hours to reach a toxic level (10 gm of caffeine is equal to about 100 cups of brewed coffee). Dangerous blood levels are more often seen with overuse of caffeine pills or tablets. [3]

Did You Know?

• Caffeine is not just found in food and beverages but in various medications. It is often added to analgesics (pain relievers) to provide faster and more effective relief from pain and headaches. Headache or migraine pain is accompanied by enlarged inflamed blood vessels; caffeine has the opposite effect of reducing inflammation and narrowing blood vessels, which may relieve the pain.
• Caffeine can interact with various medications. It can cause your body to break down a medication too quickly so that it loses its effectiveness. It can cause a dangerously fast heart beat and high blood pressure if taken with other stimulant medications. Sometimes a medication can slow the metabolism of caffeine in the body, which may increase the risk of jitteriness and irritability, especially if one tends to drink several caffeinated drinks throughout the day. If you drink caffeinated beverages daily, talk with your doctor about potential interactions when starting a new medication.

Energy Drinks

• Clark I, Landolt HP. Coffee, caffeine, and sleep: A systematic review of epidemiological studies and randomized controlled trials. Sleep medicine reviews . 2017 Feb 1;31:70-8. *Disclosure: some of HPL’s research has been supported by Novartis Foundation for Medical-Biological Research.
• Institute of Medicine (US) Committee on Military Nutrition Research. Caffeine for the Sustainment of Mental Task Performance: Formulations for Military Operations. Washington (DC): National Academies Press (US); 2001. 2, Pharmacology of Caffeine. Available from: https://www.ncbi.nlm.nih.gov/books/NBK223808/
• van Dam RM, Hu FB, Willett WC. Coffee, Caffeine, and Health.  NEJM .  2020 Jul 23; 383:369-378
• Moustakas D, Mezzio M, Rodriguez BR, Constable MA, Mulligan ME, Voura EB. Guarana provides additional stimulation over caffeine alone in the planarian model. PLoS One . 2015 Apr 16;10(4):e0123310.
• Drewnowski A, Rehm CD. Sources of caffeine in diets of US children and adults: trends by beverage type and purchase location. Nutrients . 2016 Mar;8(3):154.
• Harpaz E, Tamir S, Weinstein A, Weinstein Y. The effect of caffeine on energy balance. Journal of basic and clinical physiology and pharmacolog y. 2017 Jan 1;28(1):1-0.
• Bu FL, Feng X, Yang XY, Ren J, Cao HJ. Relationship between caffeine intake and infertility: a systematic review of controlled clinical studies.  BMC Womens Health . 2020;20(1):125.
• Zhang YP, Li WQ, Sun YL, Zhu RT, Wang WJ. Systematic review with meta‐analysis: coffee consumption and the risk of gallstone disease. Alimentary pharmacology & therapeutics . 2015 Sep;42(6):637-48.
• Hong CT, Chan L, Bai CH. The Effect of Caffeine on the Risk and Progression of Parkinson’s Disease: A Meta-Analysis. Nutrients . 2020 Jun;12(6):1860.
• Welsh EJ, Bara A, Barley E, Cates CJ. Caffeine for asthma.  Cochrane Database Syst Rev . 2010;2010(1):CD001112.
• Lee S, Min JY, Min KB. Caffeine and Caffeine Metabolites in Relation to Insulin Resistance and Beta Cell Function in US Adults. Nutrients . 2020 Jun;12(6):1783.

Last reviewed July 2020

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Spilling the Beans: How Much Caffeine is Too Much?

According to scientists at the FDA, caffeine can be part of a healthy diet for most people, but too much caffeine may pose a danger to your health.

Do you drink just one cup of coffee or tea first thing in the morning, hoping the caffeine in it will jump-start your day? Do you follow it up with a caffeinated beverage or two and then drink several more cups of coffee throughout the day?

Does it matter?

According to scientists at the FDA, caffeine can be part of a healthy diet for most people, but too much caffeine may pose a danger to your health. Depending on factors such as body weight, medications you may take, and individual sensitivity, “too much” can vary from person to person.

Learn more about caffeine in the following questions and answers.

Is it okay for kids to consume energy drinks that contain caffeine?

Energy drinks can have more than twice the caffeine in an equal amount of coffee. The American Academy of Pediatrics has stated that “there is heightened awareness of the risks of caffeine use, abuse, and even toxicity in children and adolescents.”* Consult your health care provider for advice regarding your child’s caffeine consumption.

* Sports Drinks and Energy Drinks for Children and Adolescents: Are They Appropriate? American Academy of Pediatrics June 2011

1. Which kinds of foods and beverages contain caffeine?

Caffeine can be found naturally in the plants we use to make coffee, tea and chocolate. It’s also found in some plants used as flavorings, such as guarana, or alternative teas popular in South American, such as yerba mate (Ilex paraguariensis) and Ilex guayusa.

Caffeine may also be added as an ingredient to foods and beverages.

2. How do you know how much caffeine a food or beverage contains?

Many packaged foods, including beverages and dietary supplements containing caffeine, voluntarily provide information on the label as to how much caffeine they contain. Consumers should take care when consuming for the first time a new packaged food containing added caffeine if the amount of caffeine in the food is not declared on the label.

There are several online databases that provide estimates of caffeine content of certain foods and beverages such as coffee and tea. However, the amount in these brewed beverages can vary depending on such factors as how and where the coffee beans and tea leaves were grown and processed and how the beverage product is prepared.

For reference, a 12 ounce can of a caffeinated soft drink typically contains 30 to 40 milligrams of caffeine, an 8-ounce cup of green or black tea 30-50 milligrams, and an 8-ounce cup of coffee closer to 80 to 100 milligrams. Caffeine in energy drinks can range from 40-250 mg per 8 fluid ounces.

3. If a coffee or tea says “decaffeinated,” does that mean it contains no caffeine?

No. Decaf coffees and teas have less caffeine than their regular counterparts, but they still contain some caffeine. For example, decaf coffee typically has 2-15 milligrams in an 8-ounce cup. If you react strongly to caffeine in a negative way, you may want to avoid these beverages altogether.

4. How much caffeine is too much?

For healthy adults, the FDA has cited 400 milligrams a day—that's about four or five cups of coffee—as an amount not generally associated with dangerous, negative effects. However, there is wide variation in both how sensitive people are to the effects of caffeine and how fast they metabolize it (break it down).

Certain conditions tend to make people more sensitive to caffeine’s effects, as can some medications. In addition, if you’re pregnant, trying to become pregnant, or breastfeeding, or are concerned about another condition or medication, we recommend talking to your health care provider about whether you need to limit caffeine consumption.

The FDA has not set a level for children, but the American Academy of Pediatrics discourages the consumption of caffeine and other stimulants by children and adolescents.

5. How do you know if you’ve consumed more caffeine than you can tolerate?

Over-consuming caffeine can cause:

• anxiousness
• fast heart rate
• upset stomach
• a feeling of unhappiness (dysphoria)

6. Does caffeine pose a danger to your health?

The FDA estimates toxic effects, like seizures, can be observed with rapid consumption of around 1,200 milligrams of caffeine, or 0.15 tablespoons of pure caffeine.

Pure and highly concentrated caffeine products present a significant public health threat and have contributed to at least two deaths in the United States. The FDA has taken action to protect consumers from these products.

These products, often labeled as dietary supplements, consist of pure or highly concentrated caffeine in powder or liquid forms and are often marketed in bulk packaging with up to thousands of servings per container, requiring the consumer to measure out a safe serving from what can be a toxic or even lethal amount of bulk product.

The risk of caffeine overdose increases as the concentration of caffeine in the product increases, meaning even small dosages of a highly concentrated product could lead to dangerous effects. Just one teaspoon of pure powdered caffeine can contain the same amount of caffeine as 28 cups of coffee, and a half cup of a liquid highly concentrated caffeine product contains the equivalent of more than 20 cups of coffee. These are toxic amounts that can have serious health consequences, including death.

7.  Is drinking a lot of caffeine a substitute for sleep?

No. Caffeine is a stimulant, which may cause you to be more alert and awake, but it is not a substitute for sleep. Typically, it can take 4 to 6 hours for your body to metabolize half of what you consumed. So, a cup of coffee at dinner may keep you awake at bedtime.

8. How can I cut back on caffeine without causing unpleasant side effects?

If you’re used to drinking caffeine-containing beverages every day, and want to cut back, it’s best to do so gradually. Stopping abruptly can cause withdrawal symptoms such as headaches, anxiety, and nervousness. Unlike opioid or alcohol withdrawal, caffeine withdrawal is not considered dangerous, but it can be unpleasant. You may want to talk to your health care provider about how to cut back.

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Caffeine and the Human Body

Caffeine is estimated to be the most widely used legal psychoactive drug in the world. About 85% of US adults consume caffeine daily, averaging about 135 mg per day, or about a 12 fl oz cup of coffee. This video explores what caffeine is and some ways it affects our bodies. Click the Related Article link to read the associated Patient Page.

JN Learning™ is the home for CME and MOC from the JAMA Network. Search by specialty or US state and earn AMA PRA Category 1 Credit(s) ™ from articles, audio, Clinical Challenges and more. Learn more about CME/MOC

Coffee Consumption and Incident Tachyarrhythmias

Patient information: caffeine and health, see more about.

[00:00:00] It’s estimated to be the most widely used, legal, psychoactive drug in the world. Caffeine. It’s found naturally in the seeds, fruits, nuts, or leaves of certain plants, and, in its extracted and purified form, is a bitter white powder.

[00:00:18] Caffeine is mostly consumed in beverages. For adults, most caffeine consumed is through coffee and tea. For adolescents and children, in soda and energy drinks. It’s present naturally in chocolate and also added artificially to other products such as energy shots and some over-the-counter medications.

[00:00:38] About 85% of US adults consume caffeine daily, with the average being 135 mg per day, which is about a 12 fluid ounce cup of coffee. So, let’s dig into what caffeine is and how it affects our bodies.

[00:00:54] Caffeine is a psychoactive drug classified as a stimulant. Stimulants speed up the central nervous system.

[00:01:01] Dr. Jennifer L. Temple: It makes things move faster. So, it makes your heartbeat faster. It makes your brain work faster. It just kind of wakes you up and makes the systems of your body work.

[00:01:09] Caffeine's effect as a stimulant is primarily through its effects on the brain. After a person ingests caffeine, say in their morning cup of coffee, it’s absorbed through the stomach and travels through the bloodstream, readily moving throughout the body in body water, to the brain and, in pregnant individuals, moving through the placenta to the fetus . In the brain, it binds to adenosine receptors.

[00:01:34] Dr. David N. Juurlink: If you actually look at the structure of adenosine it looks a lot like caffeine, and we can think of adenosine as, at least with regard to the nervous system, a drug that sort of slows down or turns down neuronal activity, caffeine opposes that and that's the basis, or at least a large part of the basis, for its stimulant effects.

[00:01:57] Adenosine makes us feel tired. Caffeine is an antagonist to adenosine. So caffeine binds to adenosine receptors and keeps adenosine from binding, leading to an opposite effect and stimulating alertness.

[00:02:10] And this can make people feel good.

[00:02:12] Dr. Jennifer L. Temple: There are positive effects of caffeine. It does make people feel alert. It makes people feel energetic. When we do like mood ratings, people report that they feel happier that they feel like they are, want to do things more.

[00:02:28] Blood levels of caffeine and it’s affects begin to peak around 30-60 minutes after ingestion. Caffeine has a half-life between 2.5 to 4.5 hours, which is how long it takes for the concentration of caffeine in the blood to decrease by half. But how long it stays in the body varies from person to person.

[00:02:47] While genetics are a factor in caffeine metabolism, there are other known external factors too. Cigarette smoking, and eating charcoal grilled foods and Brassica vegetables such as broccoli, brussels sprouts, and cabbage can speed up caffeine metabolism. Steroid hormones, and medications like oral contraceptives, certain antidepressants, and some cardiovascular medications and antibiotics can slow down caffeine metabolism. Pregnancy can also slow caffeine removal from the bloodstream. During the third trimester the half-life can be upwards of 10 hours .

[00:03:22] Dr. Jennifer L. Temple: But there's a lot of interindividual variability that is not easy to predict, but people who are sensitive tend to know they are sensitive.

[00:03:34] There is a lot of variability in how much caffeine is in the foods or beverages we consume, but depending on the brands and preparation, an 8 fluid ounce cup of brewed coffee contains anywhere from 102-200 mg of caffeine. Brewed tea can vary from 40 to 120 mg of caffeine in 8 fluid ounces. Depending on the brand, sodas can vary from 0-71 mgs in a 12 fluid ounce can, or about 47 mg in 8 fluid ounces.

[00:04:04] The US Food and Drug Administration cites 400 mgs of caffeine a day as, “not generally associated with dangerous, negative effects.”

[00:04:12] Dr. David N. Juurlink: Depending on the person, as you get up to 200 or 500 milligrams or more, then you start to exhibit some of the less pleasant effects: sweatiness and a bit of tremor, a bit of anxiety, or even palpitations, sort of a sensation of the awareness of your heartbeat. And there are other things that you won’t necessarily appreciate unless you’re measuring them like an increase in your heart rate or an increase in your systolic and diastolic, blood pressure. It promotes urination because caffeine is a diuretic.

[00:04:44] Caffeine consumed late in the day can also lead to difficulty falling asleep and maintaining quality sleep.

[00:04:50] Dr. David N. Juurlink: People don’t appreciate just how much of a hindrance it can be towards a healthy night’s sleep. It’s very common to encounter people who have trouble falling asleep. Ask a few questions and you’ll find out that they’re routinely in the habit of having a coffee at three or four in the afternoon.

[00:05:05] It’s worth noting that The American College of Obstetricians and Gynecologists recommends pregnant individuals limit caffeine to less than 200 mg a day. And the American Academy of Pediatrics discourages caffeine consumption in children.

[00:05:21] The effects of caffeine are most noticeable in new consumers of caffeine, but for habitual consumers it’s different. People who consume caffeine regularly may develop a tolerance, and with tolerance there is a reduced sensitivity to caffeine due to ongoing exposure.

[00:05:37] Dr. Jennifer L. Temple: Your body's always trying to maintain this homeostasis. And when you're using caffeine to make you feel awake, your body becomes dependent on that stimulation from the caffeine so that when you don't have it, you feel extra tired, extra sluggish, and you need that caffeine to just bring you back up to normal, as opposed to bringing you above normal, where you’re extra energized, or extra alert, or extra attentive. Now you're just sort of where everybody else that never drinks coffee is.

[00:06:07] Habitual caffeine consumers can eventually develop dependence on caffeine. If they stop, they might experience withdrawal symptoms, such as headaches, fatigue, depressed mood, irritability, difficulty concentrating, and flu-like symptoms. The intensity of withdrawal symptoms depends, in part, on how long and at what dose a person has been consuming caffeine.

[00:06:30] Luckily caffeine withdrawal is not dangerous, is most noticeable 1 to 2 days after stopping caffeine, and will wane in a about week . A person who wants to give up caffeine can reduce the severity of withdrawal symptoms by gradually decreasing caffeine intake over time.

[00:06:47] What can be dangerous, however, are extremely high doses of caffeine in a short period of time.

[00:06:53] Depending on sensitivity, an individual can begin experiencing more severe effects of caffeine when consuming 1200 mg or more.

[00:07:01] Dr. Jennifer L. Temple: The early toxic effects, when you've kind of gone over that hump and maybe you've had a little bit too much, people feel jittery for sure. They might feel a little bit more anxious. But nausea is a big one. Their stomachs just start to really not feel good. But if you go beyond that you do start to get vomiting and you start to get the effects on the heart. You'll start to get really rapid heartbeat. Maybe some arrhythmias there.

[00:07:28] Symptoms of caffeine toxicity can include these:

[00:07:32] But 1200 mg or more of caffeine would be a lot for the average consumer. That’s about 10 8 fluid ounce cups of brewed coffee, somewhere between 10-30 8 fluid ounce cups of tea, and about 17 cans of soda.

[00:07:47] Instances of caffeine toxicity have been related to consumption of energy drinks, energy shots, and caffeine pills consumed over a short period of time.

[00:07:56] Depending on the brand , energy drinks can vary anywhere between 160 mg to upwards of 300 mg of caffeine or more in a 16 fluid ounce can. Energy shots can pack 200 mg or more than 350 mg in 2 fluid ounces. Caffeine pills or tablets come in 100 mg or 200 mg doses.

[00:08:17] Also, consumption of caffeinated energy drinks or energy shots along with alcohol is a dangerous combination and has resulted in deaths.

[00:08:26] With how much easier it is to consume 1200 mg here, these are the products consumers should keep an eye on. But for the everyday coffee, tea, or soda consumer, it’s likely that the more subtle negative effects like jitteriness, anxiety, and heart palpitation will stop them from consuming too much caffeine. As long as individuals pay attention to these subtle signs, they can continue to consume this particular psychoactive drug safely.

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Yes, You Can Make Your Caffeine ‘Buzz’ Last Longer After Just One Cup of Coffee. Here’s Exactly How

This is even more imperative if having more than one cup of coffee irritates your stomach (hi, endless hours of acid reflux). But according to food scientists, drinking more coffee isn’t necessarily the solution to get you through a mid-day slump. In fact, there are a few ways to hack your caffeine intake to keep that energy "high" going well past your first sip of the day.

Ahead, we’re sharing seven ways to stay as energized as possible while keeping your overall caffeine intake low.

• Natalie Alibrandi , UK-based food scientist and CEO of Nali Consulting
• Trevor Craig , a food safety expert and corporate director of technical training and consulting at Microbac Laboratories

Wait, why do you feel "buzzed" from caffeine?

First things first, why does coffee (or other caffeinated beverages) make you feel buzzed to begin with? According to Natalie Alibrandi , a London-based food scientist and CEO of Nali Consulting , it’s due to a chain reaction that occurs in your brain upon ingesting caffeine.

“The caffeine ‘buzz’ is created primarily through blocking the action of adenosine, a neurotransmitter that promotes relaxation and drowsiness. Caffeine competes with adenosine for binding to its receptors in the brain, so instead we may feel increased alertness,” Alibrandi explains.

Aside from the effect caffeine has on the brain, Alibrandi says there are secondary effects it may have throughout the body, particularly on your central nervous system (CNS). “A stimulated CNS, [can lead] to an increase in heart rate and blood pressure implicated in the ‘buzz-like’ sensation,” she says.

Have jitters from too much caffeine ? Alibrandi says caffeine's stimulatory effects on the CNS are likely to blame. “Caffeine also stimulates adrenaline, which can increase heart rate, blood pressure, and energy levels. High adrenaline can lead to nervousness and jitteriness,” Alibrandi explains.

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How long does a caffeine buzz typically last?

The length of a caffeine-induced buzz can vary from person to person, but Alibrandi says the effects of caffeine can start to kick in within just 15 to 45 minutes after consumption. Meanwhile, the "peak buzz" will typically occur around the 30- to 60-minute mark post-consumption.

But you should only expect the effects of caffeine to last between three to six hours (at best). The big time gap is due to three main factors: how much caffeine is consumed, individual tolerance, and metabolism, Alibrandi says. Plus, she notes that caffeine tolerance can build up over time with regular consumption.

7 ways to make your caffeine buzz last longer

1. pair caffeine with a source of l-theanine.

According to Alibrandi, one of the best ways to make your caffeine buzz last longer is to pair it with L-theanine , an amino acid known for its ability to help enhance alertness.

“To extend a caffeine ‘high,’ stay hydrated, eat a balanced meal, and consider combining caffeine with L-theanine, that [according to] research, synergizes with caffeine for a smoother and longer-lasting buzz 1 , while reducing jitteriness,” she says.

Alibrandi notes that L-theanine is available via supplement form or can be found in caffeinated beverages like green tea.

2. Add a bit of sugar to your caffeinated beverage

While keeping in mind that consuming sugar in moderation is always important, Alibrandi says this pantry staple can potentially help prolong a caffeine buzz. “Some research suggests that sugar in energy drinks 2 may enhance caffeine's initial effects, prolonging alertness and subjective energy,” she says.

However, Alibrandi notes that this approach may not be optimal for overall health due to potential blood glucose spikes and caffeine crashes, aka the fatigue experienced after consuming too much caffeine.

3. Sip your drink slow and steady

“Drinking a caffeinated beverage over a longer period of time may help sustain a milder and more prolonged caffeine buzz compared to consuming it quickly all at once,” Alibrandi says. "This is because gradual intake allows for a slower release of caffeine into the bloodstream, potentially reducing the risk of abrupt spikes and crashes in blood sugar and energy levels,” she adds.

As such, slow and steady (caffeine intake) usually wins the race. But this, again, can vary depending on a person’s tolerance.

4. Pair your caffeine with foods high in certain nutrients

Although the influence of food on caffeine metabolism is generally considered minor compared to factors like genetics, liver function, and individual metabolism, there are a few nutrients that can potentially help prolong the effects of caffeine, Alibrandi says.

“Some foods, such as those high in antioxidants , fat, protein, and particularly foods rich in dietary fiber may have subtle effects on caffeine absorption and digestion due to their impact on gastric emptying and metabolism,” she says. But Alibrandi notes that scientific evidence supporting the significant influence of specific foods on caffeine metabolism is limited.

5. Drink coffee *after* eating breakfast

According to Alibrandi, it’s best to wait roughly 60 to 90 minutes after waking up to start consuming caffeine. “This allows for the adenosine to get flushed out and allows your body to naturally wake up before you add in caffeine,” she says.

In addition to this, Alibrandi explains that some studies suggest that consuming coffee after eating breakfast may be beneficial for several reasons. “Recent discussions suggest that consuming coffee after breakfast , rather than before, may help moderate blood glucose levels and potentially extend the duration of a caffeine-induced ‘high,’” she says. “Blood glucose spikes influence factors like general functioning, appetite, and restlessness, all of which contribute to feelings of being energized, often associated with caffeine consumption.”

That said, more research is needed on the topic to conclusively determine this relationship.

6. Choose beverages with higher caffeine concentrations

“Beverages with higher caffeine concentrations, like espresso shots and energy drinks, are absorbed quickly into the bloodstream, resulting in a stronger and longer-lasting buzz,” Alibrandi says.

She explains that their smaller volume contributes to faster absorption compared to larger (by volume) drinks like coffee or tea (if no other caffeine has been consumed already). On the flip side, lower-caffeinated beverages may yield a milder and shorter-lasting effect, she adds.

That said, Alibrandi notes that individual tolerance, again, typically plays a huge role, with regular caffeine drinkers often needing higher doses to experience the same buzz. But if there’s one thing Alibrandi wants to stress it’s that moderation is key, especially when it comes to optimizing a caffeine buzz while minimizing negative effects like jitteriness and insomnia. In other words, more caffeine might not be the solution for everyone.

7. Make a few lifestyle changes

Alibrandi says getting adequate sleep, engaging in moderate exercise, and practicing mindful caffeine consumption are also equally as important to further optimizing the effects of caffeine and duration of a buzz. However, to reiterate, more caffeine isn’t always the way to go.

“Consumption of high quantities [of caffeine] habitually may increase the likelihood of abuse of caffeine over time, further weakening the strength of a buzz,” she says.

Why drinking more caffeine isn’t always the solution for more energy

Although your initial instinct to keep the buzz going may be to drink more caffeine, Alibrandi says you may want to think twice before refilling your cup for the zillionth time in a day. Indeed, more caffeine intake can equal a longer buzz, but it comes with a few drawbacks. “The more caffeine, the more adenosine receptors are blocked, which can result in a more pronounced stimulating effect,” Alibrandi explains.

Trevor Craig , a food safety expert and corporate director of technical training and consulting at Microbac Laboratories , also adds that the average half-life of caffeine can be anywhere from two to six hours. “This means that the more you have, the longer the effects, but again the harsher the downfall would be,” Craig says.

Not to mention, there’s only so much caffeine your body can handle, Alibrandi explains. “There’s a limit to how much caffeine your body can effectively process. When the enzymes in the liver reach their limit in metabolizing caffeine, further intake won't enhance its effects,” she says.

In fact, she notes that repeated exposure to caffeine can make your body “down-regulate” or “desensitize” adenosine receptors in the brain, meaning their sensitivity to caffeine is diminished.

Plus, more caffeine intake can lead to jitteriness, increased heart rate, anxiety, and gastrointestinal discomfort that can detract from the overall buzz, she says.

Benefits of coffee, according to an RD:

• Dodd, F L et al. “A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood.”  Psychopharmacology  vol. 232,14 (2015): 2563-76. doi:10.1007/s00213-015-3895-0
• Alsunni, Ahmed Abdulrahman. “Energy Drink Consumption: Beneficial and Adverse Health Effects.”  International journal of health sciences  vol. 9,4 (2015): 468-74.
• Smith HA, Hengist A, Thomas J, Walhin JP, Heath P, Perkin O, Chen YC, Gonzalez JT, Betts JA. Glucose control upon waking is unaffected by hourly sleep fragmentation during the night, but is impaired by morning caffeinated coffee. Br J Nutr. 2020 Nov 28;124(10):1114-1120. doi: 10.1017/S0007114520001865. Epub 2020 Jun 1. PMID: 32475359.

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Health Headlines: Pros and cons of caffeine

ORLANDO, Fla. (Ivanhoe Newswire) - Caffeine is the most commonly used drug in the world. More than 90 percent of adult Americans consume caffeine regularly. But there are both benefits and risks when it comes to using this popular stimulant.

It perks you up and provides a boost of energy – but what are the benefits and drawbacks of caffeine?

On the positive side, caffeine may improve your performance during endurance exercise. It may also boost weight loss by temporarily suppressing your appetite and helping your body make more energy when digesting food. Research from Johns Hopkins shows it also may sharpen your long-term memory. And one study found that caffeine applied directly to the skin of mice helped prevent UV light from causing skin cancer. Beverages that contain caffeine, like coffee, contain powerful antioxidants.

Ashley Hinds, RDN, LDN, CEDRD, Registered Dietitian says, “There are some studies that show a lot of, actually, nutrition benefits to coffee.”

Various studies have found coffee consumption may lessen your risk of developing certain cancers, diabetes, stroke, Parkinson’s disease, and other medical conditions. But – too much caffeine can have negative consequences.

Ashley Hinds, RDN, LDN, CEDRD says, “I’m always aware of that caffeine can actually increase our anxiety and it can disrupt our sleep cycle.”

Caffeine may also affect fertility. According to a study published in the British Journal of Pharmacology, caffeine can reduce a woman’s chances of becoming pregnant by about 27 percent. And women who consume caffeine during menopause are more likely to have hot flashes and night sweats. Experts generally recommend no more than 400 milligrams a day – that’s about four, eight-ounce cups of coffee. Helping you understand the pros and cons of caffeine.

The American Academy of Pediatrics says that kids under 12 should avoid caffeine. Twelve to 18 year olds should have no more than 100 milligrams of caffeine a day. And experts advise pregnant women to consume no more than 200 milligrams a day.

Contributors to this news report include: Julie Marks, Producer; Chuck Bennethum, Editor.

Copyright 2024 KPLC. All rights reserved.

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Starbucks’s New Iced Energy Drink Has Half Your Daily Recommended Amount of Caffeine

Sometime between my senior year of college and now, I developed an inconveniently high caffeine tolerance, meaning I’m always on the lookout for a drink that will make me feel…something. So when I learned about the new Starbucks Iced Energy drinks, I was intrigued by the prospect of a beverage that just might deliver heat relief and an energy boost in a single serving.

Combining “sparkling fruit flavors with iced tea,” as the Starbucks website reads , the company’s new Iced Energy drink looks alluringly refreshing, but unlike your average smoothie or slushie, it’s pretty much packed with caffeine. According to the nutrition information available online, the 24-ounce drink contains 140 to 205 milligrams (mg) of caffeine—on par with the store’s grande, or 16-ounce, cold brew. You have three different options to choose from: Melon Burst Iced Energy, Tropical Citrus Iced Energy, and Frozen Tropical Citrus Iced Energy with Strawberry Purée (that last one can be purchased only through the Starbucks app for a limited amount of time). The Tropical Citrus flavor tips the caffeine scales the most, with 205 mg.

On an extremely hot New York day, I decided to try one to ward off the afternoon slump. I ordered a Tropical Citrus Iced Energy at a Starbucks a few minutes away from my office, and started sipping after lunch. By the time I was back at work, I had polished off about a quarter of it (which wasn’t hard to do, considering that it tasted like a fizzy iced tea). While I was sitting at my desk about half an hour later, I noticed that my concentration had improved, my heart was beating harder, and my fingers shook when I tried to hold them still—and I still had half my Tropical Citrus Iced Energy to go. Next came trouble focusing and a feeling of pressure in my head; my eyes seemed to skate over the Google doc on my computer screen. My body’s response seemed to stabilize there, but my heart rate still felt elevated when I left the office around 6:30 p.m.

So what was going on there? For one, that drink flooded my body with caffeine. The FDA recommends taking in no more than 400 milligrams per day, so one Tropical Citrus Iced Energy packs just over half of the daily max. (Plus I was already about 100 mg deep since I also had coffee that morning.) That amount puts it well above an 8.4-ounce Red Bull (80 mg) and an eight-ounce cup of coffee (typically between 80 to 100 mg), but below a 20-ounce Charged Lemonade from Panera (259 to 260 mg). According to the Associated Press , Panera recently announced it would be pulling those drinks after multiple lawsuits were filed against the company.

As someone who normally drinks maybe two cups of coffee per day (three if I’m feeling especially low-energy), I felt my reaction to the Iced Energy was especially pronounced—more so than I expected, at least. I guess it shouldn’t have been too surprising: Caffeine can cause a wide range of effects, especially if you’re sensitive to the stimulant: Think heightened alertness, increased urination, and an upset stomach or heartburn. And if you take in too much of it, you might experience anxiety, dehydration, dizziness, headaches, and insomnia.

Plus, since the drink is so cooling and tasty, you’re probably more likely to gulp it down (like I did). That’s “going to have more of an effect” than if you were to sip it slowly, like you’d do with a hot drink, Estee Glikman, RDN, CDN , a cofounder of Love & Grits Nutrition Therapy, tells SELF.

Another thing: If you’re looking for the ultimate hydration choice for these scorching summer days, this might not be it. A solid amount of electrolytes is key, Glikman says. Something that contains enough sodium, chloride, and potassium —e.g., coconut water or a sports drink—would be a better choice, as SELF reported previously. (While the Iced Energy drinks do contain sodium—35 mg each for the Melon Burst Iced Energy and the Tropical Citrus Iced Energy, and 270 mg for the Frozen Tropical Citrus Iced Energy with Strawberry Purée—the first two can’t really compare to something like a Gatorade Thirst Quencher, which contains 110 mg of potassium and 380 mg of sodium per bottle.) What’s more, “the caffeine is a diuretic and it’s actually going to work against hydration,” Glikman says.

Like I mentioned before, I’ve built up a high caffeine tolerance over the years, so I imagine my reaction to an Iced Energy drink wasn’t as strong as it could be for some folks. Children, adolescents, and people who have certain health conditions might feel the effects more, Glikman says.

Even if you don’t fall into any of those categories, Glikman recommends drinking the Iced Energy beverages in moderation—especially if you’re dipping into other sources of caffeine too. (After all, if you have a venti, or 24-ounce, iced coffee in the morning and then an Iced Energy in the afternoon, she points out, you could be “well exceeding the [FDA-recommended] amount of milligrams” per day.) When you do indulge, try to sip slowly so the caffeine doesn’t hit you all at once, eat something with it to reduce the impact, and drink (actual) water so you don’t get dehydrated. And if your goal is to rehydrate as quickly and efficiently as possible? You might want to stick to these tried-and-true ways instead.

• Here’s How Long You Should Wait to Brush Your Teeth After Your Morning Coffee
• So Is Coffee Bad for You in Any Way?
• 13 Best Instant Coffee Brands to Keep in Your Pantry

SELF does not provide medical advice, diagnosis, or treatment. Any information published on this website or by this brand is not intended as a substitute for medical advice, and you should not take any action before consulting with a healthcare professional.

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Caffeine fix: do the ‘coffee diet’ and the ‘7-second coffee loophole’ really aid weight loss.

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We love a quick fix and a new swath of coffee-inspired diets is making the rounds — or grounds, as it were — promising a lean life one cup at a time.

Coffee has long been lauded as a powerful jolt for eliminating jiggle . A recent  study  from Harvard’s T.H. Chan School of Public Health revealed that four cups of mud per day can lower body fat by approximately 4%.

The caffeine in coffee boosts metabolic rate , increasing how quickly your body burns fat, studies have found. Another smaller study found that ingesting caffeine led to a 13% increase in calorie burning and a two-fold increase in fat burning.

As of late, two caffeine-based diets, the 7-second coffee loophole and the bare-bones black cup coffee diet, have been brewing up fresh promises about the relationship between a cup of joe and a leaner life.

The 7-second coffee loophole

The 7-second coffee loophole is a viral weight loss technique that offers a simple solution to skinny. The premise is this: within seven seconds of feeling hungry, you should down a cup of coffee peppered with specific supplements or take them alongside your dirt water.

Recently, the term “7-second loophole” has been used to advertise coffee-based weight loss supplements.

Champions of the method claim that rapid coffee intake fools the body into feeling full, suppressing appetite and aiding weight loss.

Amy Shapiro MS, RD, CDN , founder and director of  Real Nutrition , tells First For Women , “Coffee itself may help with weight loss because it does slightly increase your metabolism and act as an appetite suppressant.”

The 7-second loophole is founded on the relationship between hunger hormones and caffeine intake. According to advocates, drinking black coffee stimulates adrenaline and dopamine, curbing appetite. The aim of the game is to time your coffee consumption to combat the urge to eat.

The supplements commonly included in the coffee loophole are chromium, green tea extract, capsaicin, and L-carnitine. Known as fat burners, these supplements have long been studied for their potential to support weight loss by increasing metabolic rate and promoting fat oxidation.

While certain evidence suggests they may have that potential, research is limited, and the overall impact of these so-called fat burners on sustainable weight loss is modest at best.

The Coffee Diet

The Coffee Diet is an even easier approach to making your cup of joe work for weight loss. The Coffee Diet promotes the idea that practitioners will drop pounds quickly by increasing black coffee consumption and restricting calorie intake.

The diet gained traction with the publication of Dr. Bob Arnot’s book, “The Coffee Lover’s Diet .” The book claims that adding several cups of coffee to your daily routine alongside a whole foods diet rich in fruits, veggies, whole grains and limited processed foods can amp up metabolism, curb hunger and aid anyone on their weight loss journey.

The diet calls for three cups of black coffee per day.

Practitioners of the Coffee Diet must keep their mugs free of creams and sweeteners, as research  published in  The American Journal of Clinical Nutrition  found that while drinking a cup of coffee a day aids weight loss, adding as little as a teaspoon of sugar negates the benefit entirely.

Research supports the claim that coffee can decrease body weight, body fat and BMI. As The Post previously reported , coffee contains chlorogenic acid, which has been shown to increase fat burning and may help slow the absorption of carbohydrates. Coffee consumption is linked to a variety of other health benefits.

• Coffee is rich in antioxidants that reduce oxidative stress and inflammation in the body.  
• Coffee improves focus and cognitive function, helping drinkers stay alert and productive.
• Caffeine can enhance physical performance by  increasing adrenaline levels , leading to prolonged calorie-torching sweat sessions. A better workout is linked to muscle maintenance and more caloric expenditure, both keystones for weight loss.
• Coffee can guard against serious diseases. Regular consumption has been linked to a reduced risk of several diseases, including Parkinson’s disease, Alzheimer’s disease , type 2 diabetes , and certain types of cancer.
• In several studies, coffee has been linked to longevity .

While the beans can certainly be a boon, coffee consumption does have its drawbacks, including raising blood pressure and exacerbating anxiety and sleep disorders. Still, coffee may support weight loss and offers myriad benefits to the body but a healthy diet and an active lifestyle remain the cornerstones of optimal health.

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Study finds no association between caffeine intake and invasive breast cancer risk

By David J. Hill

Release Date: September 27, 2021

BUFFALO, N.Y. — Researchers from the University at Buffalo conducted a study of nearly 80,000 postmenopausal women in the U.S. to determine whether caffeine consumption from coffee and tea has any association with invasive breast cancer.

The average age when U.S. women reach menopause, 51, also happens to coincide with the age group — 50- to 64-year-olds — that has the highest reported caffeine consumption. In addition to that, the average age of breast cancer diagnosis in the U.S. is 62.

This overlap of age at menopause, age at diagnosis of breast cancer and age with high caffeine consumption gave greater weight to the importance of clarifying whether caffeine intake impacts breast cancer risk in postmenopausal women.

It does not, according to the UB researchers’ findings, published in August in the International Journal of Cancer .

“From our literature review, many studies have found significant associations between coffee and/or tea consumption and reduced breast cancer incidence whereas a few studies have reported elevated risk. Our study, however, found no association,” said study first author Christina KH Zheng, who worked on the study while completing her master’s in epidemiology at UB. She is now a surgical resident in the MedStar Baltimore general surgery program.

“About 85% of Americans drink at least one caffeinated beverage a day. It is important for the public to know whether consumption of caffeinated beverages has beneficial or harmful effects on breast cancer, the most common type of cancer and second-leading cause of cancer death for U.S. women,” said Lina Mu , MD, PhD, the study’s senior author, who is an associate professor of epidemiology and environmental health at UB.

“The overlap of age at diagnosis of breast cancer and age with high consumption of caffeine, and the inconsistent findings from previous studies motivated us to study whether this lifestyle factor could affect breast cancer risk in postmenopausal women,” said Kexin Zhu, a study co-first author and epidemiology PhD student in UB’s School of Public Health and Health Professions.

Researchers looked at a sample of 79,871 participants in the Women’s Health Initiative Observational Study. Participants have for decades now completed yearly health questionnaires that help researchers learn more about diet and exercise habits, as well as disease, and any possible linkages.

After a median follow-up of 16 years, there were 4,719 cases of invasive breast cancer identified.

At first glance, women who reported drinking two to three cups of caffeinated coffee per day had a 12% higher risk of invasive breast cancer compared to non-drinkers. But that association was not statistically significant after adjusting for lifestyle factors, such as smoking and alcohol consumption.

“Seeing null results after adjusting for lifestyle, demographic and reproductive factors informs us of the complexity that is the relationship between caffeine intake and invasive breast cancer risk,” Zheng said.

“Some lifestyle factors, like drinking alcohol and physical activity, might be associated with both coffee intake and breast cancer risk,” Zhu explained. “Therefore, they might confound the initial positive associations. After we took the lifestyle factors into account, the results suggested that regular coffee drinking might not have an impact on invasive breast cancer risk.”

The risk of invasive breast cancer was even higher — 22% — for women who reported drinking two to three cups of decaffeinated coffee each day. It was slightly lower when adjusted for lifestyle variables (smoking history, alcohol consumption, physical activity, etc.), and the association was not statistically significant when further accounting for reproductive variables such as family history of breast cancer and number of children

The researchers were unable to determine if the elevated risk is due to the decaffeinated nature of the coffee, the amount consumed, or another factor unique to this population that was not accounted for in the study.

The researchers did not observe a significant association between overall tea consumption and invasive breast cancer. Additional research needs to be done in order to understand whether different types of teas have different effects on breast cancer risk, Zhu said.

Additional co-authors on the paper are all from UB’s Department of Epidemiology and Environmental Health and include Jean Wactawski-Wende , PhD, dean of the School of Public Health and Health Professions and SUNY Distinguished Professor; Jo L. Freudenheim , PhD, SUNY Distinguished Professor; Michael LaMonte , PhD, research professor; and Kathleen Hovey, data manager/statistician.

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David J. Hill Director of Media Relations Public Health, Architecture, Urban and Regional Planning, Sustainability Tel: 716-645-4651 [email protected]

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Clinical Assistant Professor of Finance

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Contact:  Nicole Hunter can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

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Professor of Law

Expertise:  constitutional law, election law and voting rights, and comparative constitutional law

Phone:  716-645-0558

Email: [email protected]

Sophie Nowicki

SUNY Empire Innovation Professor of Geology

Expertise:  climate change, ice sheet modeling, Greenland and Antarctic ice sheets, glaciers, sea level rise

Phone:  716-645-4335

Email:  [email protected]

Venu Govindaraju

Vice President for Research and Economic Development

Expertise:  artificial intelligence, including document analysis recognition, machine learning, pattern recognition, biometrics and generative AI

Phone:  716-645-3321

Email: [email protected]

Oscar G. Gómez-Duarte

Chief of the Division of Pediatric Infectious Diseases in the Department of Pediatrics

Expertise: pediatric infectious diseases, vaccines, childhood diarrhea, health disparities, COVID-19 community interventions

Phone:  716-323-0150. Gómez-Duarte can also be reached through Ellen Goldbaum in University Communications at 716-645-4605 or [email protected] , or Douglas Sitler in University Communications at 716-645-9069 or [email protected]

Email: [email protected]

Derek Daniels

Professor and Chair of Biological Sciences

Expertise:  science of thirst; science of food, water and salt intake; ingestive/eating behaviors

Phone:  716-645-0264

Email:  [email protected]

Xiufeng Liu

SUNY Distinguished Professor of Learning and Instruction

Expertise: STEM education, including student achievement, assessment and evaluation, and STEM teaching in colleges and universities; science and the public

Phone:  716-645-4050

Email: [email protected]

Stephanie Argentine

Executive in Residence at the Center for Leadership and Organizational Effectiveness

Expertise: employee engagement, recruitment and retention; startups and employee stock ownership plans (ESOPs); compensation and benefits; the future of work; succession planning; board governance; strategic planning

Contact: Stephanie Argentine can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Greg A. Valentine

UB Distinguished Professor of Geology

Expertise: volcanoes, volcanic eruptions, disaster preparedness, supervolcanoes

Phone:  716-645-4295

Email: [email protected]

Alan Rabideau

Professor and Chair of Civil, Structural and Environmental Engineering

Expertise: pollution, groundwater contamination, radioactive and hazardous waste management, mathematical modeling

Phone: 716-645-4003

Email:  [email protected]

Assistant Professor of Civil, Structural and Environmental Engineering

Expertise: air pollution, greenhouse gases, climate change, remote sensing, molecular spectroscopy

Phone:  716-645-6167

Email: [email protected]

Marc Halfon

Professor of Biochemistry

Expertise: genetics; gene expression; gene drive; genome editing; mosquito genome; cell growth, differentiation and development

Phone:  716-829-3126

Email: [email protected]

Clayton Masterman

Associate Professor of Law

Expertise:  Health law, tort law, benefit-cost analysis, damages and other remedies, law and economics

Phone:  716-645-2480

Email:  [email protected]

Stefan Ruhl

Professor of Oral Biology

Expertise:  saliva, oral bacteria, glycobiology of bacterial adhesion, oral microbiome, oral health

Phone:  716-829-6073

Email:  [email protected]

Associate Professor of Epidemiology and Environmental Health

Expertise: air pollution, cancer, particulate matter, environmental epidemiology, air pollution in China

Phone:  716-829-5381

Email: [email protected]

Allison Brashear

Vice President for Health Sciences and Dean of the Jacobs School of Medicine and Biomedical Sciences at the University at Buffalo

Expertise:  medical education and research, diversity in medicine, women in medicine, community engagement and health equity, clinical trials, treatment of rare neurologic disorders, spasticity and dystonia.

Contact: Allison Brashear can be reached through Ellen Goldbaum in University Communications at 716-645-4605 or [email protected] .

Expertise:  surveillance and disinfection of pathogens in wastewater and the environment; wastewater-based disease monitoring; environmental microbiology; proteomics

Phone:  716-645-4002

Email:   [email protected]

Timothy Hellwig

Professor of Political Science

Expertise:  politics of European nations, the European Union, immigration and trade in Europe, the US, and globally, public support for presidents and governments around the world. 

Phone:  716-645-8440

Email: [email protected]

Athena D. Mutua

Professor of Law and Floyd H. and Hilda L. Hurst Faculty Scholar

Expertise: civil rights law; constitutional law (Fourteenth Amendment); critical race and feminist legal theory; law and political economy; race and the legal justice system

Phone:  716-645-2873. Athena D. Mutua can sometimes be contacted more quickly through the UB Media Relations team at [email protected] .

Email: [email protected]

Helen A. “Nellie” Drew

Director of the Center for the Advancement of Sport

Expertise:  sports law, including student-athletes’ name, image and likeness (NIL), antitrust laws, collective bargaining, discipline of athletes, drug testing, NCAA compliance and Title IX; diversity in sport

Phone:  716-645-2071

Email: [email protected]

Melinda Lemke

Associate Professor of Educational Leadership and Policy

Expertise:  K-12 educational policy and reform; politics of education; public health; sociocultural contexts of education

Phone:  716-645-1090

Email:  [email protected]

Stephanie Fredrick

Associate Director of the Alberti Center for Bullying Abuse Prevention

Expertise:  bullying, cyberbullying, youth mental health, bullying interventions

Phone:  716-645-1141

Email:  [email protected]

Robert Miletich

Interim Chair and Professor of Nuclear Medicine

Expertise: nuclear medicine, nuclear neurology, brain scans and other neuroimaging techniques and neurodegenerative diseases

Phone:  716-838-5889

Email: [email protected]

Despina Stratigakos

Professor of Architecture

Expertise:  diversity in architecture; gender and modernity in European cities; German architecture; Nazi propaganda and architecture

Phone: 716-829-3486

Email: [email protected]

Jason Benedict

Associate Professor of Chemistry

Expertise: chemistry, chemical reactions, chemical crystallography, photochemistry, nanomaterials, synchrotron light sources, science of snowflakes

Phone:  716-645-4276

Email: [email protected]

Ghazala Saleem

Assistant Professor of Rehabilitation Science

Expertise:  concussions (especially in children), traumatic brain injury, brain injury and intimate partner violence

Phone:  716-829-2589

Email:  [email protected]

David Doermann

SUNY Empire Innovation Professor of Computer Science and Engineering

Expertise:  artificial intelligence, pattern recognition, machine learning, deep learning, computer vision, image analysis and recognition, document analysis, media forensics

Phone:  716-645-1557

Email: [email protected]

Priya R. Banerjee

Associate Professor of Physics

Expertise: intrinsically disordered proteins, protein droplets, membrane-less organelles, single-molecule biophysics

Phone:  716-645-3444

Email: [email protected]

Margaret Rhee

Assistant Professor of Media Study

Expertise:  digital storytelling; participatory art; new media, ethnic, cultural, Asian American, queer and feminist studies

Phone:  716-645-0923

Email:  [email protected]

Luis A. Colón

A. Conger Goodyear Professor of Chemistry

Expertise: analytical chemistry, separation science, liquid chromatography, diversity in STEM, mentoring students of color

Phone:  716-645-4213

Email: [email protected]

Conor Dowling

Expertise:  U.S. elections, public opinion, campaign finance, political parties, effects of political scandal

Phone:  716-645-8436

Email: [email protected]

John J. Leddy

Director of the Concussion Management Clinic

Expertise:  concussions, post-concussion syndrome, sports medicine

Phone: 716-829-5501

Email: [email protected]

Joshua J. Lynch

Clinical Associate Professor of Emergency Medicine

Expertise: addiction medicine; opioid crisis; telemedicine and medication-assisted treatment and linkage to care for people with substance use disorders; critical care transport

Email:  [email protected]

Contact: Joshua J. Lynch can also be reached through Ellen Goldbaum in University Communications at 716-645-4605 or  [email protected] , or Douglas Sitler in University Communications at 716-645-9069 or  [email protected] .

Associate Professor of Accounting and Law

Expertise: corporate voluntary disclosures; accounting fraud; environmental, social and governance (ESG) accounting; mergers and acquisitions (consolidation) accounting; executive and employee turnover; accounting-marketing interface

Contact:  Inho Suk can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Thomas A. Russo

Chief of the Division of Infectious Diseases in the Department of Medicine

Expertise: infectious diseases; superbugs; antibiotic resistance; drug and vaccine development

Phone:  716-829-2674. Russo can also be reached through Ellen Goldbaum in University Communications at 716-645-4605 or  [email protected] , or Douglas Sitler in University Communications at 716-645-9069 or  [email protected]

Email: [email protected]

Kenneth Joseph

Associate Professor of Computer Science and Engineering

Expertise:  computing for social good; societal impacts of social media and online platforms (including in news and politics); inequality and societal divides; artificial intelligence

Phone:  716-645-0682

Email:  [email protected]

Joanne Song McLaughlin

Associate Professor of Economics

Expertise: labor economics; health insurance mandates; age discrimination; older workers; AI and the future of work

Phone:  716-645-8685

Email: [email protected]

Bina Ramamurthy

Professor of Teaching in Computer Science and Engineering

Expertise: Blockchain; blockchain and cryptocurrency (Bitcoin, Ether) and non-fungible tokens; data-intensive computing; big data platforms

Phone:  716-645-3182

Email: [email protected]

Shira Gabriel

Professor of Psychology

Expertise: social psychology, social connections, sense of self, the need to belong, comfort food

Phone:  716-645-0227

Email: [email protected]

Sanjukta Smith

Associate Professor and Chair of Management Science and Systems

Expertise: online social networks, cloud computing, data center operations

Contact:  Sanjukta Smith can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Associate Professor of Psychology

Expertise: self, self-esteem, motivation, interpersonal processes

Phone: 716-645-0228

Email: [email protected]

Ian Bradley

Assistant Professor of Civil, Structural and Environmental Engineering 

Expertise:  wastewater treatment, algae, algal blooms in the Great Lakes and elsewhere

Phone:  716-645-4004

Email:   [email protected]

Heidi Julien

Professor of Information Science

Expertise: digital literacy, information literacy, information behavior, information practice

Phone: 716-645-1474

Email: [email protected]

John M. Violanti

Research Professor of Epidemiology and Environmental Health

Expertise: police stress, health and suicide; PTSD

Phone:  716-829-5481

Email: [email protected]

Negar Elhami-Khorasani

Associate Professor of Civil, Structural and Environmental Engineering

Expertise: structural fire engineering, wildfires in wildland-urban interface communities, fire following earthquake, multi-hazard engineering, disaster resilience

Phone:  716-645-3019

Email: [email protected]

Karl Fiebelkorn

Emeritus Senior Associate Dean for Student, Professional, and Community Affairs

Expertise:   laws and regulations affecting pharmacy practice, medication errors, systems for improving practice sites, adult asthma, pharmacy business plan modeling

Phone: 716-645-2824

Email: [email protected]

Kari J. Winter

Professor of American Studies

Expertise:  gender, feminism, race, class, slavery, politics of food, literature

Phone:  716-645-0827

Email:  [email protected]

Indranil Goswami

Assistant Professor of Marketing

Expertise: motivation and self-control; incentive policies; charitable giving and pro-social behavior; cognitive biases; deadlines and procrastination; judgment and decision-making; market research; consumer behavior

Contact: Indranil Goswami can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Timothy Cook

Professor of Chemistry

Expertise: molecular self-assembly, photochemistry, fluorescence, phosphorescence, batteries, alternative energy

Phone:  716-645-4327

Email: [email protected]

Larry White

Assistant Professor of Information Science

Expertise: library management, leadership, policy, organizational performance  

Phone:  716-645-1473

Email: [email protected]

John D. Atkinson

Expertise:  sustainability, greenhouse gas emissions, air and water pollution control, materials science and engineering, adsorption, life-cycle assessment

Phone:  716-645-4001

Email:  [email protected]

Marion Werner

Professor of Geography

Expertise:  global trade; agriculture, food, labor rights and trade; agri-business; development in Latin America and the Caribbean

Phone:  716-645-0475

Email:  [email protected]

Gwynn Thomas, PhD

Chair and Associate Professor of Global Gender and Sexuality Studies

Expertise:  gender and politics; feminism; global women’s movements, including #MeToo; politics in Latin America

Phone:  716-645-0793

Email:  [email protected]

Amy Reynolds

Expertise: multicultural issues, college student mental health

Phone:  716-645-1112

Email: [email protected]

Matilde Sanchez-Pena

Assistant Professor of Engineering Education

Expertise:  engineering education, cultures of wellbeing, institutional diversity, faculty advancement, equity in the engineering field, women in STEM, intersectionality

Phone:  716-645-5861

Email:  [email protected]

Wooksoo Kim

Associate Professor of Social Work

Expertise:  immigration; refugee resettlement, acculturation; social determinants of health of Asian immigrants; community-based participatory research

Phone:  716-645-1227

Email:  [email protected]

Patricia Logan-Greene

Expertise: violence and victimization, adverse childhood experiences, gun violence and prevention, child maltreatment

Phone:  716-645-1533

Email: [email protected]

Melanie Green

Chair and Professor of Communication

Expertise:  persuasion, power of narrative, storytelling, online friendships, trust and deception online

Phone:  716-645-1508

Email:  [email protected]

Brian Tsuji

Professor of Pharmacy Practice

Expertise:  superbugs, antibiotic-resistant bacteria, antibiotics

Phone:  716-881-7543

Email:  [email protected]

Phillips Stevens Jr.

Associate Professor of Anthropology

Expertise:  cultural anthropology, religion, spiritualism, cults, superstition, witchcraft, zombies, vampires, curses, rites of passage, populism, nativism, xenophobia

Phone:  716-645-0416

Email: [email protected]

Murali Ramanathan

Professor of Pharmaceutical Sciences

Expertise: multiple sclerosis (MS), disease-modifying drugs

Phone:  716-645-4846

Email: [email protected]

Susan Spierre Clark

Assistant Professor of Environment and Sustainability

Expertise:  climate change and sustainable development; resilient infrastructure; power outages due to extreme events; sustainability education; community resilience

Phone:  716-645-1403

Email:  [email protected]

Chair of Accounting and Law

Expertise: financial reporting; mergers and acquisitions; intangibles; corporate governance; insider trading

Contact:  Feng Gu can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Larry Zielinski

Executive in Residence for Health Care Administration in the School of Management

Expertise: business and economics of health care; health care delivery, innovation and reforms; health insurance reimbursement models

Contact: Larry Zielinski can be reached most quickly through Jackie Ghosen in the School of Management Communications Office at 716-645-2833 or [email protected] .

Claire E. Cameron

Expertise: early childhood education, childhood development, educational psychology, classroom management

Phone:  716-645-4075

Email: [email protected]

Yotam Ophir

Assistant Professor of Communication

Expertise: misinformation; persuasion; effect of media content on audiences, including in health, science, politics and terrorism

Phone:  716-645-1158

Email: [email protected]

Stelios Andreadis

SUNY Distinguished Professor of Chemical and Biological Engineering

Expertise: regenerative medicine, tissue engineering, stem cells, vascular grafts

Phone:  716-645-1202

Email: [email protected]

Sarah A. Robert

Expertise: teaching as an occupation; teachers’ unions; labor issues in education; global education reform; gender and equity in education; school food

Phone:  716-645-4046

Email: [email protected]

Blaine Pfeifer

Professor of Chemical and Biological Engineering

Expertise: metabolic engineering; biosynthesis of antibiotics and other compounds; vaccine design and delivery

Phone:  716-645-1198

Email: [email protected]

Andrew Whittaker

SUNY Distinguished Professor of Civil, Structural and Environmental Engineering

Expertise: earthquake engineering; seismic protective systems; blast engineering; bridge engineering; infrastructure; design and assessment of nuclear power plants; performance-based engineering; risk engineering

Phone: 716-645-4364

Email:  [email protected]

Ifeoma Nwogu

Expertise: artificial intelligence, including machine learning and human behavior; computer vision and facial expressions, and gestures and sign languages

Phone:  716-645-1588

Email:  [email protected]

Tiffany Karalis Noel

Clinical Assistant Professor of Learning and Instruction

Expertise: sociocultural inequity in education, teacher preparation and retention, mentoring in higher education

Email: [email protected]

Kristin Poinar

Assistant Professor of Geology

Expertise: climate change, Greenland Ice Sheet, ice sheet modeling, sea level rise, Antarctica, Great Lakes ice cover

Phone:  716-645-4286

Email: [email protected]

Professor of Environment and Sustainability

Expertise:  environmental movement in the U.S., environmental history, Earth Day, sustainable business, suburban sprawl

Phone:  716-645-8665

Email:  [email protected]

Richard Salvi

SUNY Distinguished Professor Emeritus of Communicative Disorders and Sciences

Expertise: tinnitus, hearing, noise-induced hearing loss, hyperacusis, central auditory system

Phone:  716-829-5310

Email: [email protected]

David Castillo

Professor of Romance Languages and Literatures

Expertise: early modern culture, Baroque literature, horror and fantasy, new media and culture

Phone: 716-645-0869

Email: [email protected]

UB on Futurity.org

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06-28-2024 NEWS

Livestreaming platform Caffeine closes, despite big media support

Caffeine’s interactive livestreaming platform for sports and entertainment was not yet profitable.

[Photos: Getty Images]

BY  Madeline Nguyen 2 minute read

Caffeine, an interactive livestreaming platform for sports and entertainment, suddenly shut down Wednesday after receiving nearly $300 million in investments from companies like Fox, Disney, and Cox.

The social livestreaming service, which launched in 2016, announced on its website that it was shutting down because it was “still not quite profitable” and would be determining its “next steps.” The service had billed itself as an alternative to the video-game-centric livestreaming service Twitch, and also allowed viewers to watch content together—regardless of distance—primarily live sports, entertainment, esports, and competitions.

According to Caffeine’s Wednesday announcement, the platform ultimately grew to four million users per day and 61 million per month.

“We’ve had a huge impact on the industry and will again soon, in a different way,” Caffeine’s website post stated.

In 2018, 21st Century Fox invested $100 million in the then-startup, in addition to a joint venture by the two companies called Caffeine Studios. Through the joint venture, 21st Century Fox said it would create exclusive content broadcasted on Caffeine, and its chairman, Lachlan Murdoch, would join the streaming platform’s board.

That same year, Caffeine also started streaming live concerts on its service after striking a deal with entertainment company Live Nation. The streaming service also received investments from Disney after Caffeine took part in the 2018 Disney Accelerator program, by which Disney gives resources to innovative companies.

“We want to bring the world together around friends and live broadcasts,” Ben Keighran, Caffeine’s CEO and cofounder, said at the time. “It’s an ambitious goal, but one we believe is attainable with the support of our amazing new partners, our awesome and ever-growing community, and the content that, together, we can bring onto the platform.”

In 2020, Fox invested in Caffeine again, in addition to the cable company Cox and various other firms, as a part of a $113 million funding round raised by the streaming service.

As a startup, Caffeine aimed to differentiate itself from its livestreaming competitors, YouTube and Twitch, by offering ad-free livestreams and allowing broadcasters to earn money through microtransactions. In recent years, Caffeine pivoted to center more on live sports. 

By the time of its shutdown, Caffeine announced that it had formed 200 partnerships with different niche sports leagues, sports creators, competitive event organizers, and sports media publishers to stream content across 17 sports categories. 

In February, it was announced that the streaming service had partnered with the LIV Golf league to broadcast coverage of its tournaments and original programs to a “younger, more diverse audience than many traditional broadcasting platforms,” according to a statement by LIV Golf. 

Caffeine’s shutdown left the league without one of its primary paid streaming rights partners despite having six events left in its 2024 campaign, LIV Golf spokesperson Doug Mayer wrote. Fast Company has reached out to Caffeine for comment.

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Caffeine TV, one of LIV's streaming partners, shuts down

Upstart sports streamer Caffeine TV has "abruptly closed, citing lagging profits just months after securing" LIV Golf’s digital broadcasting rights, according to James Colgan of GOLF. The announcement marks the “latest jarring development in an unfriendly media rights environment for LIV.” The league’s events, aired on the CW in a revenue-sharing agreement, have suffered "low TV audiences since the league signed a two-year pact" with the net in 2023, and the streaming world has “not been much friendlier.” LIV Golf had “very little to do with Caffeine TV’s financial situation,” which was tied “primarily to the startup’s struggles to properly chart its profits with investors.” However, few people knew about the streamer when LIV Golf announced the deal in February , and those who “did knew of it primarily as a home for niche sports like the World Surfing League.” Caffeine’s closure leaves LIV Golf "without a paid streaming rights partner" in the U.S. with six events remaining this year. LIV Golf does have other streaming options -- it "brought its streaming rights direct-to-consumer in 2022 and 2023 with a subscription-based product on YouTube ... and has continued to use those services after inking the Caffeine TV deal" ( GOLF, 6/26 ).

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Starbucks introduces caffeinated iced drinks. Flavors include melon, tropical citrus

Starbucks unveiled a new drink lineup, which they're calling 'iced energy.' they come in three flavors and have between 140 and 205 milligrams of caffeine, about the same as a typical cold brew.

Starbucks has dropped a new line of summery drinks that contain about the same amount of caffeine as a typical cold brew.

The sugar-free beverages, which became available at locations nationwide on Tuesday, are made with “sparkling fruit flavors and iced tea," according to a news release.

Starbucks Iced Energy drinks can be ordered in three flavors: Melon Burst, Tropical Citrus and Frozen Tropical Citrus made with Strawberry Puree.  

Melon Burst and Tropical Citrus Iced Energy drinks will be available year-round while the third flavor will only be available for a limited time this summer and can only be ordered through the Starbucks app. 

Here’s what we know about the new energy drinks and the other goodies set to be offered through the summer.

Caffeine content of Melon Burst, Tropical Citrus and Frozen Tropical Citrus drinks

The caffeine content per Iced Energy drink, which only come in 24-ounce sizes, is detailed below. Additional nutritional information, including calories per serving, can be found online or on the app or in-store. 

• Melon Burst: Melon and cucumber flavoring mixed with bright Passion Tango tea. Caffeine content: 180 milligrams
• Tropical Citrus: Passionfruit and citrus flavoring mixed with green tea. Caffeine content: 205 milligrams
• Frozen Tropical Citrus: Passionfruit and citrus flavoring combined with swirls of strawberry puree. Caffeine content: 140 milligrams

Customers also have the ability to customize their Starbucks Iced Energy drink with any tea, lemonade, or juice but will not be able to make modifications that contain caffeine. 

Brewed coffee, espresso, and refreshers cannot be added to any Starbucks Iced Energy, a Starbucks spokesperson told USA TODAY. 

How Starbucks Iced Energy differs from Panera Charged Lemonade

The release of Starbucks Iced Energy comes nearly two months after Panera Bread pulled its line of Charged Lemonade drinks off its menu amid controversy surrounding the caffeine contents in those drinks, USA TODAY reported. Drinks, that according customer allegations, resulted in permanent health issues or death. 

The caffeine content of the new Starbucks drinks varies but the range is between 140 and 205 milligrams, depending on the size, according to Starbucks. 

A 24-ounce Iced Energy drink has a similar caffeine content as a 16-ounce cold brew beverage, Starbucks says. 

The drinks have between 120 and 185 fewer milligrams of caffeine than the discontinued Charged Lemonade from Panera. While the highest caffeine content in the new Starbucks drinks is 205 milligrams, the highest in the Panera Charged Lemonade was almost double at 390 milligrams.

The recommended daily amount of caffeine for adults is between 300 and 400 milligrams, which is equal to about four to five cups of coffee, USA TODAY reported. 

Starbucks drinks, other menu items also make summer debut 

Iced Energy drinks aren’t the only menu items making their summer debut.

Starbucks has also announced the arrival of a couple other new beverages and treats, including a  nondairy vanilla sweet cream, a nondairy vanilla sweet cream cold foam and a Caramel Vanilla Swirl Iced Coffee. 

All of these new drinks and treats, including the Egg, Pesto and Mozzarella Sandwich and the Blueberry Streusel Muffin, will be available year-round.