Safe ceiling by age, weight, and pregnancy status.
What does the daily caffeine limit mean?
Caffeine is the world's most widely consumed psychoactive substance. It works by blocking adenosine receptors in the brain, adenosine is a neurotransmitter that promotes sleep, and caffeine's blocking action produces wakefulness, alertness, and improved concentration. It also stimulates the sympathetic nervous system, raising heart rate and blood pressure modestly.
The FDA states that 400 mg/day is an amount "not generally associated with dangerous, negative effects" for healthy adults. The EFSA, in a 2015 scientific opinion, similarly concluded that 400 mg/day is safe for healthy non-pregnant adults, and that single doses up to 200 mg are safe consumed up to 2 hours before intense physical activity. For pregnant women, ACOG recommends limiting caffeine to below 200 mg/day due to evidence of association with miscarriage and restricted fetal growth at higher intakes.
For children and adolescents, the picture is different. Caffeine metabolism is faster in children than adults (relative to body weight), but the effects on sleep, anxiety, and the developing brain are a concern. The AAP does not recommend caffeinated beverages for children or adolescents. EFSA suggests 3 mg/kg/day as the upper limit for children.
Individual sensitivity to caffeine varies substantially. About 10–15% of the population are "fast metabolisers" due to a CYP1A2 genetic variant, while "slow metabolisers" may experience cardiovascular effects at lower doses. Caffeine half-life averages 5 hours but ranges from 2 to 12 hours, which explains why some people can drink coffee at 8pm and sleep at midnight while others cannot.
Reference limits by population
| Population | Daily caffeine limit |
|---|---|
| Healthy adults | ≤ 400 mg/day (FDA/EFSA) |
| Pregnant women | ≤ 200 mg/day (ACOG) |
| Children / adolescents | < 2.5 mg/kg/day (EFSA); AAP advises none |
| Pre-exercise (acute safe single dose) | ≤ 200 mg (EFSA) |
When should you see a doctor?
If you have heart arrhythmias, anxiety disorders, GERD, or take medications that interact with caffeine (including some antibiotics, adenosine, and certain asthma medications), discuss your intake with your doctor. During pregnancy, err on the side of caution and review all caffeine sources including tea, chocolate, cola, and medications containing caffeine. If you experience palpitations, chest discomfort, severe anxiety, or insomnia related to caffeine, reducing intake gradually and consulting a doctor is advisable.