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.
Frequently asked questions
How much caffeine is safe per day?
The FDA and EFSA conclude that up to 400 mg of caffeine per day is safe for healthy non-pregnant adults. This is approximately 4 cups of brewed coffee (each ~95mg). During pregnancy, ACOG recommends limiting caffeine to below 200 mg/day. Children and adolescents should consume less than 2.5 mg/kg body weight per day (equivalent to roughly 65 mg for a typical 12-year-old).
How much caffeine is in common drinks?
Approximate caffeine content: brewed coffee 240mL/8oz = 80–120mg, espresso single shot = 60–70mg, black tea 240mL = 40–70mg, green tea 240mL = 25–45mg, cola 355mL/12oz = 34–46mg, energy drink 250mL = 70–80mg, dark chocolate 30g = 12–25mg. Amounts vary significantly by brand, brewing method, and serving size.
Is caffeine bad for you?
In moderate amounts (up to 400 mg/day), caffeine is safe and may be beneficial for most adults. It improves alertness, concentration, and athletic performance. However, excessive intake causes anxiety, insomnia, palpitations, headache, and elevated blood pressure. Caffeine is mildly addictive, and withdrawal causes headaches and fatigue. Sensitivity varies widely between individuals due to genetic differences in caffeine metabolism.