Caffeine is a stimulant found naturally in coffee, tea and cacao, and added to soft drinks, energy drinks, pre-workout products and over-the-counter alertness tablets. In sport it is sold mostly as caffeine anhydrous, a dried powder pressed into tablets or capsules.
It is one of the few supplements with strong evidence for a performance benefit. The International Olympic Committee (IOC) lists it among a small group of supplements, with creatine, nitrate and bicarbonate, that have good evidence of benefit (Maughan et al., BJSM 2018). The benefits are small to moderate, vary a lot between people, and come with trade-offs in sleep, anxiety and blood pressure. Caffeine is not prohibited in sport; WADA only monitors it.
This page summarizes what position stands, meta-analyses, the FDA and WADA report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Class | Methylxanthine stimulant; adenosine receptor antagonist |
| Chemistry | 1,3,7-trimethylxanthine; C₈H₁₀N₄O₂; 194.19 g/mol (PubChem) |
| Common sources | Coffee, tea, soft drinks, energy drinks, pre-workout supplements, OTC alertness tablets |
| US OTC drug dose | 100–200 mg, not more often than every 3–4 h (21 CFR 340.50) |
| Studied ergogenic dose | 3–6 mg/kg body mass, most often about 60 min before exercise (ISSN 2021, IOC 2018) |
| Half-life | Usually 4–6 h in adults, but reported from 1.5 to 10 h (ISSN 2021) |
| Metabolism | Over 95% by the liver enzyme CYP1A2, mainly to paraxanthine |
| FDA intake reference | 400 mg/day cited as not generally linked to negative effects in most adults |
| WADA 2026 | In the Monitoring Program; not a prohibited substance |
What it is
Caffeine is a purine alkaloid, chemically 1,3,7-trimethylxanthine (PubChem). It is related to theophylline (an asthma drug) and theobromine (the main stimulant in cocoa), which are also two of its breakdown products.
Its main action is to block adenosine receptors. Adenosine builds up in the brain during waking hours and promotes drowsiness, so blocking it increases alertness. The IOC consensus lists several mechanisms that may explain the performance effect (Maughan et al., BJSM 2018):
- adenosine receptor antagonism;
- increased endorphin release;
- improved neuromuscular function;
- improved vigilance and alertness;
- reduced perception of effort during exercise.
The amount in common drinks varies widely. FDA lists these typical ranges per 12 fl oz (355 mL) (FDA, Spilling the Beans):
| Drink | Typical caffeine per 12 fl oz |
|---|---|
| Caffeinated soft drink | 23–83 mg |
| Green tea | 37 mg |
| Black tea | 71 mg |
| Brewed coffee (regular, non-specialty) | 113–247 mg |
| Energy drink | 41–246 mg |
FDA also notes that decaffeinated coffee is not caffeine-free: a typical 8 fl oz cup has 2–15 mg. The body handles caffeine the same way whether it comes from coffee or is added to a product.
Related library pages cover L-theanine, the tea amino acid that is often paired with caffeine, and other stimulants such as synephrine and ephedrine.
Pharmacokinetics
Caffeine is absorbed quickly from the gut, mainly from the small intestine but also from the stomach (Guest et al., JISSN 2021). The ISSN position stand reports these points:
| Parameter | What the ISSN reports |
|---|---|
| Absorption | Rapid, mainly small intestine; caffeine gum is also absorbed through the lining of the mouth, which may be faster |
| Time to peak | In one small study (n = 3) with 160 mg: about 0.5 h for coffee and tea, 2 h for cola |
| Main enzyme | CYP1A2 in the liver, which handles over 95% of caffeine |
| Primary metabolites | Paraxanthine ≈84%, theobromine ≈12%, theophylline ≈4% |
| Excreted unchanged in urine | About 3–5% |
| Half-life | Generally 4–6 h; may range from 1.5 to 10 h in adults |
Why the half-life varies so much
CYP1A2 activity differs widely between people, so the same dose can last much longer in one person than in another (Nehlig, Pharmacol Rev 2018). The ISSN lists the main factors (Guest et al., JISSN 2021):
- Slower clearance: pregnancy and hormonal contraceptives.
- Faster clearance: cigarette smoking and heavy habitual caffeine use, which induce CYP1A2.
- Either direction: some dietary factors, and variation in the CYP1A2 gene.
The best-studied gene variant is the -163A>C polymorphism (rs762551). People with the AA genotype are often called “fast metabolizers,” and C-allele carriers “slow metabolizers.” Nehlig’s review also notes that caffeine clearance is affected by age, sex hormones, liver disease, obesity and many medications.
Regulatory status
- Food ingredient. FDA does not have a regulation specific to “energy drinks.” Packaged foods must list caffeine in the ingredients when it is added on its own, but restaurants are not required to say how much caffeine their drinks contain (FDA, Spilling the Beans).
- OTC drug. Caffeine is the only active ingredient allowed in US OTC “alertness aid” or “stimulant” products. The labeled adult dose is 100–200 mg, not more often than every 3–4 hours, “for occasional use only,” and the products are not for children under 12 (21 CFR 340).
- Pure and highly concentrated caffeine. FDA considers bulk pure or highly concentrated caffeine sold as a dietary supplement a significant public health threat (see Side effects below).
What the research shows
Position stands
The ISSN position stand (2021) concluded that caffeine (Guest et al., JISSN 2021):
- acutely improves many types of exercise performance “in many but not all studies,” with small to moderate benefits for muscular endurance, movement speed, muscular strength, sprinting, jumping and throwing;
- gives the most consistent, moderate-to-large benefits in aerobic endurance;
- consistently improves performance at 3–6 mg/kg body mass, with a minimum effective dose possibly as low as 2 mg/kg;
- at very high doses such as 9 mg/kg causes many side effects without being needed for a benefit;
- is most often taken about 60 minutes before exercise, though gum may need a shorter wait;
- works in both trained and untrained people, and improves attention and vigilance in most people.
The IOC consensus statement (2018) gives a similar summary (Maughan et al., BJSM 2018):
| Topic | IOC summary |
|---|---|
| Typical protocol | 3–6 mg/kg caffeine anhydrous about 60 min before exercise |
| Lower-dose option | Under 3 mg/kg (about 200 mg) before and during exercise, with carbohydrate |
| Endurance | Improves time to fatigue and time trials of 5–150 min across cycling, running, rowing and other modes |
| Low doses during exercise | 100–300 mg taken after 15–80 min of activity may improve cycling time trials by 3–7% |
| Short, high-intensity work | 3–6 mg/kg taken 50–60 min before gives gains of over 3% in 1–2 min anaerobic tasks, and 1–8% in team-sport repeated sprints |
| Higher doses | 9 mg/kg or more does not add benefit and raises the risk of nausea, anxiety, insomnia and restlessness |
| Fluid balance | Caffeine is a diuretic, but the effect is small at performance doses |
Two caveats apply. The ISSN statement’s authors disclosed many ties to supplement companies, and the ISSN itself has received grants from companies selling caffeine products. And in an umbrella review of the meta-analyses, most of the underlying trials were done in young men (Grgic et al., BJSM 2020).
Overview of meta-analyses
An umbrella review pooled 11 systematic reviews containing 21 meta-analyses (Grgic et al., BJSM 2020). It found that:
- caffeine was ergogenic for aerobic endurance, muscle strength, muscle endurance, power, jumping and speed;
- the evidence for muscle endurance, muscle strength, anaerobic power and aerobic endurance was of moderate quality; for other outcomes it was low or very low;
- the effect was generally larger for aerobic than for anaerobic exercise;
- not every analysis gave a definite direction of effect once the 95% prediction interval was considered.
Strength and power
A 2018 meta-analysis pooled placebo-controlled trials that measured 1-repetition maximum (1RM) strength (10 studies) and vertical jump power (10 studies) (Grgic et al., JISSN 2018):
| Outcome | Standardized mean difference vs placebo (95% CI) |
|---|---|
| Maximal strength (1RM), overall | 0.20 (0.03–0.36) |
| Upper-body strength | 0.21 (0.02–0.39) |
| Lower-body strength | 0.15 (−0.05 to 0.34), not significant |
| Power (vertical jump) | 0.17 (0.00–0.34) |
An effect size around 0.2 is conventionally called small. For strength training, caffeine’s effect is real but modest.
Endurance
A 2022 meta-analysis pooled 21 randomized crossover trials of endurance running with 254 participants, at caffeine doses of 3–9 mg/kg (Wang et al., Nutrients 2022):
| Outcome | Hedges’ g (95% CI) | Size |
|---|---|---|
| Time to exhaustion, all runners | 0.392 (0.214–0.571) | Medium |
| Time to exhaustion, recreational runners | 0.469 (0.185–0.754) | Medium |
| Time to exhaustion, trained runners | 0.344 (0.122–0.566) | Medium |
| Time-trial completion time | −0.101 (−0.190 to −0.012) | Small (faster) |
Only 19 of the participants were women, so the authors called for more research in women and on the best dose.
Genetics and individual response
The largest trial of caffeine and CYP1A2 genotype randomized 101 competitive male athletes to placebo, 2 mg/kg or 4 mg/kg caffeine before a 10-km cycling time trial (Guest et al., MSSE 2018):
| Group | 2 mg/kg | 4 mg/kg |
|---|---|---|
| All athletes | — | 3% faster than placebo |
| AA genotype (“fast metabolizers”) | 4.8% faster | 6.8% faster |
| AC genotype | No effect | No effect |
| CC genotype (“slow metabolizers”) | No effect | 13.7% slower |
These results have not been consistent across studies. The ISSN notes that other, smaller trials found no effect of CYP1A2 genotype or a benefit only in slow metabolizers (Guest et al., JISSN 2021). The ISSN also lists habitual caffeine intake as a possible factor in individual response. The first author of both papers consults for a genetic testing company, as disclosed in the position stand.
Side effects and risks
How much is too much
FDA has cited 400 mg/day, about two to three 12-fl-oz cups of coffee, as an amount “not generally associated with negative effects” for most adults (FDA, Spilling the Beans). FDA adds that sensitivity and elimination speed vary widely between people, and that some conditions and medications increase sensitivity.
A systematic review of studies from 2001 to 2015 reached similar conclusions (Wikoff et al., Food Chem Toxicol 2017):
| Population | Intake the review found generally not linked to adverse effects |
|---|---|
| Healthy adults | Up to 400 mg/day |
| Healthy pregnant women | Up to 300 mg/day (reproductive and developmental effects) |
| Children and adolescents | 2.5 mg/kg/day (limited data) |
FDA advises people who are pregnant, trying to become pregnant or breastfeeding to ask their health care provider whether to limit caffeine. It also notes that medical experts advise against energy drinks for children and teens.
Common effects of too much caffeine
FDA lists these signs of excess caffeine (FDA, Spilling the Beans):
- fast heart rate and palpitations;
- high blood pressure;
- insomnia or sleep disruption;
- anxiety and jitters;
- upset stomach and nausea;
- headache.
In exercise studies, side effects such as nausea, anxiety, fast heart rate and insomnia become more common at 9 mg/kg or more, a dose that gives no extra benefit (Maughan et al., BJSM 2018). FDA notes that withdrawal after cutting back is unpleasant but not considered dangerous, and recommends reducing gradually.
Pure and highly concentrated caffeine
This is the most serious documented risk. According to FDA (FDA, Pure and Highly Concentrated Caffeine; FDA, Spilling the Beans):
- pure and highly concentrated caffeine products have contributed to at least two deaths in the US;
- one teaspoon of pure powdered caffeine can contain as much caffeine as 28 cups of coffee, and half a cup of a concentrated liquid product more than 20 cups;
- toxic effects such as seizures can occur with rapid intake of about 1,200 mg, less than half a teaspoon of pure powder;
- the gap between a safe and a toxic amount is very small, and kitchen measuring spoons are not accurate enough to measure a safe serving;
- toxicity can cause a dangerously fast or erratic heartbeat, seizures, vomiting, diarrhea, stupor, disorientation and death.
FDA issued warning letters to distributors of pure powdered caffeine from 2015 onward and, in April 2018, issued industry guidance explaining when such dietary supplements are considered adulterated and illegal. FDA states that some of these products remain on the market. The IOC consensus describes two separate incidents in university research in which dose-calculation errors led to volunteers receiving very large doses, up to 30 g, with adverse and potentially fatal responses (Maughan et al., BJSM 2018).
Sleep
- Meta-analysis. A 2023 meta-analysis of 24 studies found that caffeine reduced total sleep time by 45 min and sleep efficiency by 7%, lengthened the time to fall asleep by 9 min, and increased wake time after falling asleep by 12 min. Deep sleep (N3 and N4) fell by 11.4 min (Gardiner et al., Sleep Med Rev 2023). From their model, the authors estimated that a coffee (107 mg) should be taken at least 8.8 h before bed, and a typical pre-workout serving (217.5 mg) at least 13.2 h before bed, to avoid losing sleep time.
- Timing trial. In 12 healthy sleepers, 400 mg of caffeine taken at bedtime, 3 h before bed or 6 h before bed significantly disturbed sleep compared with placebo at every time point. Taken 6 h before bed, it reduced objectively measured sleep by 41 min, a difference that approached statistical significance (Drake et al., J Clin Sleep Med 2013).
The ISSN notes that sensitivity to caffeine’s effects on sleep differs between people, partly because of genetic variation (Guest et al., JISSN 2021).
Blood pressure
Caffeine raises blood pressure, and the effect is larger with caffeine tablets than with coffee.
- Regular intake. A meta-analysis of 16 randomized trials (1,010 participants, at least 7 days each) found that pure caffeine at a median 410 mg/day raised blood pressure by 4.16/2.41 mmHg. Coffee raised it by only 1.22/0.49 mmHg. Effects on heart rate were negligible (Noordzij et al., J Hypertens 2005).
- People with hypertension. In 5 trials, a single 200–300 mg dose raised blood pressure by 8.1/5.7 mmHg (95% CI 5.7–10.6 systolic; 4.1–7.4 diastolic). The rise appeared within the first hour and lasted at least 3 h. Longer-term coffee trials (2 weeks) and cohort studies did not show higher blood pressure or cardiovascular disease with habitual coffee drinking (Mesas et al., Am J Clin Nutr 2011).
Interactions
- Other stimulants. Some products combine caffeine with other stimulants such as synephrine, yohimbine or DMAA. FDA advises counting caffeine from all sources (FDA, Spilling the Beans).
- Medications. Because CYP1A2 handles nearly all caffeine metabolism, caffeine interacts with many medications that use or affect this enzyme (Nehlig, Pharmacol Rev 2018).
- Hormonal contraceptives and pregnancy slow caffeine clearance, and smoking speeds it up (Guest et al., JISSN 2021).
Legal status and use in sport
Caffeine is not a prohibited substance under the WADA 2026 Prohibited List. The list names caffeine, together with bupropion, nicotine, phenylephrine, phenylpropanolamine, pipradrol and synephrine, as included in the 2026 Monitoring Program and “not considered Prohibited Substances.” Under the Monitoring Program, WADA tracks caffeine concentrations in urine samples collected after competition (Aguilar-Navarro et al., Nutrients 2019). By contrast, under the same list, ephedrine is prohibited in competition when its urine concentration exceeds 10 µg/mL.
This was not always the case. Caffeine was banned by the IOC and other anti-doping bodies from 1984 to 2004, in competition only, with a urine threshold of 12 µg/mL set in 1987. WADA removed it from the prohibited list from January 1, 2004 (Aguilar-Navarro et al., Nutrients 2019). In 7,488 Spanish doping-control samples, median urine caffeine rose only slightly from 2004 (0.70 µg/mL) to 2015 (0.85 µg/mL), with the highest 2015 levels in cycling, athletics and rowing.
Key takeaways
- One of the best-supported supplements. The ISSN and IOC agree that caffeine improves endurance and, to a smaller degree, strength, power and sprint performance.
- Studied doses are 3–6 mg/kg. Doses of 9 mg/kg or more add side effects without extra benefit; the minimum effective dose may be as low as 2 mg/kg.
- Effects are modest and vary. Strength effects are small (SMD about 0.2), and response differs between people, possibly in part because of CYP1A2 genotype, though findings are inconsistent.
- Half-life is usually 4–6 h but can reach 10 h. Caffeine taken even 6 h before bed can measurably reduce sleep.
- Blood pressure rises, especially with tablets. Pure caffeine at about 400 mg/day raised blood pressure by about 4/2 mmHg in trials, more than coffee did.
- Powder is the real danger. FDA links pure and highly concentrated caffeine to at least two US deaths; around 1,200 mg taken quickly can cause seizures. Caffeine is legal in sport and only monitored by WADA.
Sources
- Guest NS, VanDusseldorp TA, Nelson MT, et al. International society of sports nutrition position stand: caffeine and exercise performance. J Int Soc Sports Nutr. 2021;18(1):1. PubMed; PMC.
- Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7):439–455. PubMed; PMC.
- Grgic J, Grgic I, Pickering C, et al. Wake up and smell the coffee: caffeine supplementation and exercise performance-an umbrella review of 21 published meta-analyses. Br J Sports Med. 2020;54(11):681–688. PubMed.
- Grgic J, Trexler ET, Lazinica B, Pedisic Z. Effects of caffeine intake on muscle strength and power: a systematic review and meta-analysis. J Int Soc Sports Nutr. 2018;15:11. PubMed.
- Wang Z, Qiu B, Gao J, Del Coso J. Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-Analysis. Nutrients. 2022;15(1):148. PubMed.
- Guest N, Corey P, Vescovi J, El-Sohemy A. Caffeine, CYP1A2 Genotype, and Endurance Performance in Athletes. Med Sci Sports Exerc. 2018;50(8):1570–1578. PubMed.
- Nehlig A. Interindividual Differences in Caffeine Metabolism and Factors Driving Caffeine Consumption. Pharmacol Rev. 2018;70(2):384–411. PubMed.
- Gardiner C, Weakley J, Burke LM, et al. The effect of caffeine on subsequent sleep: A systematic review and meta-analysis. Sleep Med Rev. 2023;69:101764. PubMed.
- Drake C, Roehrs T, Shambroom J, Roth T. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013;9(11):1195–1200. PubMed.
- Noordzij M, Uiterwaal CS, Arends LR, et al. Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens. 2005;23(5):921–928. PubMed.
- Mesas AE, Leon-Muñoz LM, Rodriguez-Artalejo F, Lopez-Garcia E. The effect of coffee on blood pressure and cardiovascular disease in hypertensive individuals: a systematic review and meta-analysis. Am J Clin Nutr. 2011;94(4):1113–1126. PubMed.
- Wikoff D, Welsh BT, Henderson R, et al. Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food Chem Toxicol. 2017;109(Pt 1):585–648. PubMed.
- Food and Drug Administration. Spilling the Beans: How Much Caffeine is Too Much? Consumer Update; content current as of August 28, 2024. FDA.
- Food and Drug Administration. Pure and Highly Concentrated Caffeine. Content current as of March 6, 2023. FDA.
- Code of Federal Regulations. 21 CFR Part 340: Stimulant drug products for over-the-counter human use. eCFR.
- World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2026. WADA 2026 Prohibited List.
- Aguilar-Navarro M, Muñoz G, Salinero JJ, et al. Urine Caffeine Concentration in Doping Control Samples from 2004 to 2015. Nutrients. 2019;11(2):286. PubMed.
- National Center for Biotechnology Information. PubChem Compound Summary for CID 2519, Caffeine. PubChem.