Caffeine: how much is too much, and what it does

Caffeine is usually judged by the cup, as if every coffee held the same dose. Single espressos bought from 97 cafes held anywhere from 25 to 214 mg, and the measured effects in trials are modest: a blood pressure rise of about 2 mmHg and a small gain in exercise performance.

How much you need

• US survey coding puts brewed coffee at 40 mg caffeine per 3.5 oz (100 g), so an 8 fl oz cup carries 96 mg and a large 600 g cup 240 mg. — FNDDS food Coffee, brewed Evidence E source
• Single espressos bought from 97 cafes held 106 mg caffeine on average, but ranged from 25 to 214 mg per serve. — 97 espresso samples from commercial vendors, Gold Coast, Australia Evidence C source
• US national surveys put usual caffeine intake at 25 mg a day in children aged 2-11 and 50 mg a day in teens aged 12-17. — US children and adolescents, NHANES 2007-2010 and Kantar beverage panel Evidence C source
• Caffeinated drinks sold in US high schools held 63 mg on average, with school coffee at 103 mg and energy drinks at 95 mg. — 45 middle and 45 high schools, national US sample Evidence C source

Who is most likely to fall short

• EFSA judges up to 400 mg a day safe for healthy adults but sets 200 mg a day for pregnancy. — healthy adults; pregnant women Evidence E source
• The Nordic Nutrition Recommendations 2023 review links high caffeine intake in pregnancy to pregnancy loss, preterm birth and low birth weight, and keeps the EFSA 200 mg a day ceiling. — scoping review of qualified systematic reviews for NNR 2023 Evidence C source
• Observational meta-analyses link caffeine or coffee in pregnancy to 34% higher odds of low birth weight. — 13 systematic reviews with 15 meta-analyses of cohort, case-control and cross-sectional studies Evidence C source
• Observational data link higher caffeine intake in teenagers aged 12-18 to 67% higher odds of sleep problems. — adolescents aged 12-18; meta-analysis subgroup of 6 studies, mostly cross-sectional Evidence C source

What the evidence does and does not show

• Across 19 crossover RCTs in 235 women, caffeine gave a small cycling performance gain (SMD 0.21), with high certainty of evidence. — 235 females in 19 randomized crossover trials Evidence A source
• In 26 crossover RCTs of female team-sport athletes, caffeine gave a small physical performance benefit (g 0.32), most for repeated sprints, agility and sprint speed. — female team-sport athletes, 26 randomized placebo-controlled crossover trials Evidence A source
• In 21 placebo-controlled studies, caffeine lengthened time to exhaustion on a maximal exercise test (SMD 0.41) and raised peak minute ventilation (SMD 0.33). — 21 studies of maximal graded exercise tests Evidence A source
• In 12 studies with 666 people, caffeine improved cycling time trials only in carriers of the CYP1A2 A allele, by 0.90 units, with no effect in C allele carriers. — 666 participants in 12 studies genotyped for CYP1A2 rs762551 Evidence B source
• Rinsing the mouth with caffeine without swallowing did not significantly improve intermittent sprint exercise across 20 crossover RCTs (SMD 0.37, CI crossing zero). — 20 randomized crossover studies of high-intensity intermittent exercise Evidence A source
• The EU refused the claim that caffeine enhances physical performance or delays fatigue. — EU Register on nutrition and health claims, snapshot 2026-09-21 Evidence E source
• The EU also refused the claim that 40-75 mg of caffeine per serving helps increase alertness. — EU Register on nutrition and health claims, snapshot 2026-09-21 Evidence E source
• In a double-blind crossover RCT of 30 men, 5 mg/kg caffeine a day for four days did not change hydration status measured by urine specific gravity. — 30 men aged 20-39 with low habitual caffeine intake (<100 mg/day) Evidence B source
• Across 21 cohorts with 10 million people, 3 cups of coffee a day was linked to 13% lower all-cause mortality, and decaf showed a similar link. — 21 cohort study articles, 10,103,115 participants, 240,303 deaths Evidence C source
• In 131,821 US adults followed up to 43 years, the highest caffeinated coffee intake was linked to 18% lower dementia risk, and decaf showed no such link. — Nurses' Health Study and Health Professionals Follow-up Study, 131,821 participants, median 36.8 years Evidence C source

What too much does

• The FDA cites 400 mg a day, about two to three 12 fl oz cups of coffee, as an amount not generally linked to negative effects in most adults. — most adults Evidence E source
• In a meta-analysis of 8 RCTs in adults, caffeine supplements raised systolic blood pressure by 1.94 mmHg and diastolic by 1.66 mmHg. — adults 18+ in 8 RCTs (11 effect sizes) Evidence A source
• In a randomized crossover study, coffee with 127 mg caffeine after 2 days off raised brachial systolic pressure by 7.6 mmHg and diastolic by 4.9 mmHg over the next 4 hours. — middle-aged normotensive subjects after 2 days without caffeine; 2 x 10 fl oz (300 ml) black coffee, felodipine 10 mg Evidence B source
• The FDA estimates that toxic effects such as seizures can appear with rapid intake of around 1,200 mg of caffeine, less than half a teaspoon of pure powder. — general population Evidence E source
• A 46-year-old man who swallowed 10 g of caffeine developed arrhythmia, diabetic ketoacidosis and stomach injury, and survived. — single patient, 46-year-old man Evidence D source

Medicines it interacts with

• In a small dosing study, two women on oral contraceptives cleared caffeine about three times more slowly, with a half-life of 15.5 hours versus 5.6 hours. — 8 healthy adults, single oral dose with 200 mg caffeine; 2 taking oral contraceptives Evidence C source

What to do with this

The cup tells you little about the dose. US survey coding puts brewed coffee at 40 mg per 3.5 oz (100 g), which works out to 96 mg in an 8 fl oz cup and 240 mg in a large 600 g cup, values recalculated from 100 g that real brews will miss. Single espressos from 97 cafes in one Australian region held 106 mg on average and ranged from 25 to 214 mg.

For healthy adults, the FDA cites 400 mg a day, about two to three 12 fl oz cups of coffee, as an amount not generally linked to negative effects, and EFSA judges up to 400 mg a day safe. In pregnancy, EFSA sets 200 mg a day, and the Nordic recommendations keep the same ceiling. Observational studies link caffeine or coffee in pregnancy to 34 percent higher odds of low birth weight, an association that trials have not tested.

Pure caffeine powder is the real hazard. The FDA estimates that rapid intake of around 1,200 mg can cause toxic effects such as seizures, and that is less than half a teaspoon of powder.

A break from caffeine changes the response. In middle-aged volunteers with normal blood pressure, coffee with 127 mg after 2 days off raised systolic pressure by 7.6 mmHg over the next 4 hours, in a trial whose size the abstract does not give.

If you are pregnant, take regular medicines or use oral contraceptives, how much caffeine fits is a question for the person treating you. We have no card on a safe daily level for children and teenagers, so the 400 mg figures apply to adults only. Apart from oral contraceptives, which slowed caffeine clearance about threefold in two women, we have no card on how caffeine interacts with medicines.

Where to get it from food

USDA does not report caffeine for individual foods, so this site cannot rank foods by it. The sections above name the foods the studies themselves looked at.

The bottom line

Caffeine does measurable things in small amounts. It raised blood pressure by about 2 mmHg across 8 trials of supplements and gave a small gain in cycling and team-sport performance in trials of women. In a four-day trial in 30 men with low habitual intake, it did not change hydration status. In cohort studies, coffee drinking went with lower all-cause mortality and, for caffeinated coffee, lower dementia risk. These are associations, and decaf showed a similar link to mortality. The cautions are pregnancy, teenagers' sleep and concentrated powder.

Sources

1. cafn-daily-r1-19 · Position of an expert body · USDA FNDDS, dataset
   Coffee, brewed (FDC 2710375): Caffeine 40 MG per 100 g; 1 cup (8 fl oz) 240 g 96.0 MG; 1 small 360 g 144.0 MG; 1 medium 480 g 192.0 MG; 1 large 600 g 240.0 MG (value from the source's table, not a sentence)
   USDA FNDDS, Coffee, brewed (FDC 2710375) · checked 2026-10-02 · independently re-checked
2. cafn-daily-r1-15 · Observational data · cross-sectional
   The mean (+/-SD) quantity of caffeine was 106+/-38 mg/serve with a concentration of 2473+/-1092 mg/l. There was considerable variation in caffeine content. The range per serve was 25-214 mg whilst the concentration range was 580-7000 mg/l.
   Food Chem Toxicol, 2007 · checked 2026-10-02 · independently re-checked
3. cafn-daily-r1-16 · Observational data · survey review
   The usual intakes of caffeine were 25 and 50 mg/d for children and adolescents aged 2-11 and 12-17 y, respectively (NHANES 2007-2010).
   Adv Nutr, 2015 · checked 2026-10-02 · independently re-checked
4. cafn-daily-r1-17 · Observational data · cross-sectional
   On average, caffeinated beverages contained 63 mg of caffeine. The most common caffeinated beverages were sodas, but coffee (103 ± 25 mg) and energy drinks (95 ± 14 mg) contained the highest caffeine levels.
   J Acad Nutr Diet, 2025 · checked 2026-10-02 · independently re-checked
5. cafn-daily-r1-24 · Position of an expert body · agency position
   Intakes up to 400mg per day (about 5.7mg/kg bw per day) consumed throughout the day do not raise safety concerns for healthy adults in the general population, except pregnant women....Caffeine intakes from all sources up to 200mg per day consumed throughout the day do not raise safety concerns for the foetus.
   EFSA, Caffeine topic page (scientific opinion 2015) · checked 2026-10-02 · independently re-checked
6. cafn-daily-r1-12 · Observational data · scoping review
   High caffeine intake in pregnancy is associated with higher risk of pregnancy loss, preterm birth, and low birth weight...Pregnant women should not exceed the recommended daily dose of caffeine intake of 200 mg set by the European Food Safety Authority as a safe level for the fetus.
   Food Nutr Res, 2024 · checked 2026-10-02 · independently re-checked
7. cafn-daily-r1-11 · Observational data · umbrella review
   The following 13 maternal factors were identified as risk factors for low birth weight: crack/cocaine (odds ratio [OR] 2.82, 95% confidence interval [CI] 2.26-3.52), infertility (OR 1.34, 95% CI 1.2-1.48), smoking (OR 2.00, 95% CI 1.76-2.28), periodontal disease (OR 2.41, 95% CI 1.67-3.47), depression (OR 1.84, 95% CI 1.34-2.53), anemia (OR 1.32, 95% CI 1.13-1.55), caffeine/coffee (OR 1.34, 95% CI 1.14-1.57)
   BMC Pregnancy Childbirth, 2024 · checked 2026-10-02 · independently re-checked
8. cafn-daily-r1-10 · Observational data · meta-analysis of observational studies
   The meta-analysis further substantiated that adolescents with higher caffeine intake faced increased odds of sleep problems (OR = 1.67, 95% CI: 1.28-2.17), while alcohol consumption was significantly associated with insomnia (OR = 1.17, 95% CI: 1.07-1.27).
   Sleep Med, 2024 · checked 2026-10-02 · independently re-checked
9. cafn-daily-r1-02 · Meta-analysis or systematic review · meta-analysis
   The pooled analysis revealed a small and significant ergogenic effect of caffeine supplementation on cycling performance for females (standardized mean difference = 0.21; 95% confidence interval [0.11, 0.29]), with high certainty of evidence.
   Int J Sport Nutr Exerc Metab, 2026 · checked 2026-10-02 · independently re-checked
10. cafn-daily-r1-06 · Meta-analysis or systematic review · meta-analysis
    For physical performance, caffeine showed a small favorable effect (g = 0.32, 95% CI 0.22 to 0.42), with statistical evidence for repeated sprint ability (g = 0.43), agility or change in direction (g = 0.42), sprint or speed performance (g = 0.39), anaerobic power (g = 0.30), and jumping performance (g = 0.29).
    Nutrients, 2026 · checked 2026-10-02 · independently re-checked
11. cafn-daily-r1-03 · Meta-analysis or systematic review · meta-analysis
    Compared to placebo, caffeine increased peak minute ventilation (SMD = 0.33; p = 0.01) and time to exhaustion (SMD = 0.41; p = 0.01).
    Crit Rev Food Sci Nutr, 2024 · checked 2026-10-02 · independently re-checked
12. cafn-daily-r1-04 · Randomized controlled trial(s) · meta-analysis
    In subgroup analyses, acute caffeine intake improved cycling time trial only in individuals with the A allele (WMD = -0.90, 95%CI: -1.48 to -0.33, p = 0.002), but not the C allele (WMD = -0.08, 95%CI: -0.32 to 0.17, p = 0.53).
    J Sport Health Sci, 2024 · checked 2026-10-02 · independently re-checked
13. cafn-daily-r1-05 · Meta-analysis or systematic review · meta-analysis
    Overall, our meta-analysis revealed no significant improvement in overall HIIE performance following CHO mouth rinse (standardized mean difference = 0.18; 95% confidence interval [-0.10, 0.46]; p = .21), CAF mouth rinse (standardized mean difference = 0.37; 95% confidence interval [-0.02, 0.75]; p = .06), and CHO + CAF combined mouth rinse (standardized mean difference = -0.19; 95% confidence interval [-0.68, 0.30]; p = .44).
    Int J Sport Nutr Exerc Metab, 2026 · checked 2026-10-02 · independently re-checked
14. cafn-daily-r1-20 · Position of an expert body · EU claim register
    POL-HC-6841 Caffeine -Enhances physical performance. -Provides a performance edge -Can delay the onset of fatigue -Can increase exercise intensity/work rate Non-authorised (value from the source's table, not a sentence)
    EU Register on nutrition and health claims, claim POL-HC-6841, snapshot 2026-09-21 · checked 2026-10-02 · independently re-checked
15. cafn-daily-r1-21 · Position of an expert body · EU claim register
    POL-HC-8450 Caffeine Caffeine helps to increase alertness* * For intakes of caffeine between 40 mg per serving and 75 mg per serving -/- Non-authorised (value from the source's table, not a sentence)
    EU Register on nutrition and health claims, claim POL-HC-8450, snapshot 2026-09-21 · checked 2026-10-02 · independently re-checked
16. cafn-daily-r1-09 · Randomized controlled trial(s) · RCT, crossover
    USG values remained stable, indicating no changes in hydration status (p > 0.05).
    Clin Nutr ESPEN, 2025 · checked 2026-10-02 · independently re-checked
17. cafn-daily-r1-14 · Observational data · meta-analysis of cohorts
    Compared with no or rare coffee consumption, with a consumption of 3 cups day-1 , the risk of all-cause mortality might reduce 13% (RR = 0.87; 95% confidence interval = 0.84-0.89)...Similar inverse associations are found for caffeinated coffee and decaffeinated coffee.
    J Hum Nutr Diet, 2019 · checked 2026-10-02 · independently re-checked
18. cafn-daily-r1-13 · Observational data · cohort
    After adjusting for potential confounders and pooling results across cohorts, higher caffeinated coffee intake was significantly associated with lower dementia risk (141 vs 330 cases per 100 000 person-years comparing the fourth [highest] quartile of consumption with the first [lowest] quartile; hazard ratio, 0.82 [95% CI, 0.76 to 0.89])
    JAMA, 2026 · checked 2026-10-02 · independently re-checked
19. cafn-daily-r1-22 · Position of an expert body · agency position
    For most adults, the FDA has cited 400 milligrams a day — that's about two to three 12-fluid-ounce cups of coffee — as an amount not generally associated with negative effects.
    US FDA, Spilling the Beans: How Much Caffeine is Too Much?, 2024 · checked 2026-10-02 · independently re-checked
20. cafn-daily-r1-01 · Meta-analysis or systematic review · meta-analysis
    The pooled of 11 effect sizes analysis of 8 studies demonstrated significant increases in SBP (WMD:1.94 mmHg; 95%CI:0.52, 3.35; p = 0.007) and DBP (WMD:1.66 mmHg; 95% CI:0.75, 2.57; p = 0.000) after caffeine supplementation.
    Clin Nutr ESPEN, 2023 · checked 2026-10-02 · independently re-checked
21. cafn-daily-r1-08 · Randomized controlled trial(s) · RCT, crossover
    After coffee, blood pressure changes (mm Hg) averaged over study hours 1-4 were increased for brachial systolic (7.6, P < 0.001) and diastolic (4.9, P < 0.001) and aortic systolic (7.4, P < 0.001), pulse (3.0, P < 0.05) and augmentation (1.4, P < 0.05) relative to baseline.
    Am J Hypertens, 2016 · checked 2026-10-02 · independently re-checked
22. cafn-daily-r1-23 · Position of an expert body · agency position
    The FDA estimates toxic effects, like seizures, can be observed with rapid consumption of around 1,200 milligrams of caffeine, or less than 1/2 teaspoon of pure caffeine.
    US FDA, Spilling the Beans: How Much Caffeine is Too Much?, 2024 · checked 2026-10-02 · independently re-checked
23. cafn-daily-r1-18 · Mechanistic or laboratory data · case report
    We report the case of a 46-year-old man without a known medical history who ingested 10 g of caffeine to attempt suicide. He presented with impaired consciousness, arrhythmia, hyperglycemia, and metabolic acidosis.
    JCEM Case Rep, 2026 · checked 2026-10-02 · independently re-checked
24. cafn-daily-r1-07 · Observational data · pharmacokinetic study
    Two subjects who were taking oral contraceptives had longer caffeine half-lives (15.5 +/- 0.3 hours versus 5.6 +/- 1.7 hours) and lower values for oral clearance (0.34 +/- 0.01 mL/min. kg versus 0.99 +/- 0.41 mL/min. kg) than subjects who were not taking oral contraceptives.
    Clin Pharmacol Ther, 2002 · checked 2026-10-02 · independently re-checked