Evidence explainerCaffeine (capsules, gum and anhydrous powder)
How Much Caffeine Is Too Much? 400 mg a Day, 100 mg for Teens, and Why Pure Powder Is Dangerous
The limits are clearer than most people think, and they come from FDA and medical groups rather than guesswork. The biggest danger is not coffee but pure powdered caffeine.
Key takeaways
- FDA says 400 mg/day of caffeine does not usually have dangerous adverse effects in healthy adults [1].
- The American Medical Association recommends adults limit caffeine to 500 mg/day and adolescents to no more than 100 mg/day [1].
- Heavy use of 500 mg/day or more may diminish performance and disturb sleep [1].
- One tablespoon of pure powdered caffeine holds 10 g, and 10 to 14 g can be fatal [1].
- Combining caffeine with other stimulants could raise the risk of side effects [1].
Safety at a glance
From our Caffeine (capsules, gum and anhydrous powder) monograph. Published interactions and cautions only, each with its source.
Interactions
- Other stimulants. Combining caffeine with other stimulants could increase the potential for adverse effects.[1]
Who should be careful
- High intakes. Heavy use (500 mg/day or more) may impair rather than enhance performance and can disturb sleep and cause irritability, anxiety, restlessness, nausea, vomiting, fast heart rate and irregular rhythm. FDA says 400 mg/day is not usually linked to dangerous effects in healthy adults.[1]
- Pure powdered caffeine. Powdered caffeine is extremely potent: a tablespoon holds about 10 g, and 10–14 g can be fatal. Deaths have been reported.[1]
- Children and teens. The American Medical Association advises adolescents to keep caffeine to 100 mg/day or less, and the American Academy of Pediatrics says caffeinated energy drinks have no place in children's or adolescents' diets.[1]
- Before you start. Talk to your pharmacist or clinician before adding this supplement, especially if you take prescription medicines, are pregnant or breastfeeding, or have a chronic health condition.[1]
Full Caffeine (capsules, gum and anhydrous powder) safety section
The evidence, graded
Pulled from our monograph evidence tables. Grades follow our evidence-grading policy.
- Grade BImprovedTime-trial performance by caffeine dose and delivery formLow-dose capsules reduced completion time (SMD -0.34; 95% CI -0.62 to -0.06), followed by moderate-dose capsules (-0.31) and moderate-dose gum (-0.30); low-dose capsules also raised mean power output (SMD 0.38).
- Grade CMixedPerformance response by CYP1A2 genotypeCaffeine improved performance in AA (SMD 0.30) and AC (SMD 0.16) genotypes but worsened it in CC (SMD -0.22). After excluding studies with a risk of conflict of interest, genotype no longer mattered.
The limits for adults
For healthy adults, FDA states that 400 mg/day of caffeine does not usually have dangerous adverse effects [1]. The American Medical Association recommends that adults limit caffeine to 500 mg/day [1].
For context, a performance dose of 3 to 6 mg/kg is 210 to 420 mg for a 70 kg adult, so a performance dose on top of the rest of the day's caffeine can approach or pass 400 mg [1]. Read labels: energy drinks, shots and gels all carry caffeine [1].
Signs you have had too much
ODS lists these side effects of caffeine:
Teens and children
The American Medical Association recommends that adolescents consume no more than 100 mg/day of caffeine [1]. The American Academy of Pediatrics warns that caffeinated energy drinks have no place in the diets of children or adolescents and are not suitable during routine physical activity [1].
Why pure caffeine powder is different
Pure powdered caffeine is sold as a supplement and is very potent: a single tablespoon contains 10 g of caffeine, and an oral dose of 10 to 14 g can be fatal [1]. At least two young men have died after taking an unknown amount of it [1].
The gap between a useful dose and a dangerous one is a matter of a kitchen measuring spoon, which is why powder is a poor way to dose caffeine at home.
Why some people feel it more
Caffeine has a half-life of about 4 to 5 hours, so afternoon caffeine is still active in the evening [1]. Responses also differ between people: in a 2024 meta-analysis, people with the CYP1A2 CC genotype performed worse with caffeine, though the group was small (34 people) and the effect disappeared after excluding studies with possible conflicts of interest [2].
For how to use caffeine for exercise without overdoing it, see caffeine before a workout and the caffeine monograph.
Quick answers
Is 400 mg of caffeine at once too much?
FDA's 400 mg figure is per day for healthy adults [1]. In exercise trials, more than about 6 mg/kg was unlikely to help further and raised the risk of side effects [1].
Why is caffeine powder so risky?
It is sold as a dietary supplement but is extremely potent: a tablespoon holds 10 g, within the 10 to 14 g range that can be fatal [1].
How much caffeine can athletes have in competition?
WADA does not limit caffeine; the IOC allows urine levels up to 12 mcg/mL and the NCAA prohibits more than 15 mcg/mL, which about 500 mg can produce within 2 to 3 hours [1].
Keep reading
Full monographs
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References
- [1]Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health Professionals. NIH Office of Dietary Supplements, 2024.
- [2]Caffeine, CYP1A2 Genotype, and Exercise Performance: A Systematic Review and Meta-analysis. Med Sci Sports Exerc, 2024.