Caffeine is a stimulant found naturally in coffee, tea and cocoa, and added to soft drinks, energy drinks, supplements and some medicines. In the US it is also an over-the-counter drug: caffeine tablets are labeled as alertness aids. FDA says it can be part of a healthy diet for most people, but too much can be harmful.
Also known as: caffeine anhydrous.
FDA has cited 400 mg a day, about two to three 12-ounce cups of coffee, as an amount not generally associated with negative effects for most adults. Over-the-counter caffeine alertness aids are labeled at 100 to 200 mg, no more often than every 3 to 4 hours, for adults and children 12 and over.
FDA's consumer update says sensitivity varies widely, and that pregnancy, breastfeeding, some conditions and some medicines are reasons to ask a clinician about limits. It gives typical amounts per 12 ounces of 113 to 247 mg for brewed coffee, 71 mg for black tea and 41 to 246 mg for energy drinks. Signs of too much include fast heart rate, palpitations, high blood pressure, poor sleep, anxiety, jitters, upset stomach and headache. FDA estimates toxic effects such as seizures with rapid intake of about 1,200 mg, less than half a teaspoon of pure powder, and warns that pure and highly concentrated caffeine products can cause serious harm, including death.
The federal over-the-counter rule for caffeine alertness aids requires the label to say they are for occasional use, are not a substitute for sleep, and are not for children under 12. Caffeine is often paired with L-theanine; if you log both, log each one separately.
FDA notes wide variation in how fast people clear caffeine. A 2022 analysis of 141 pharmacokinetic studies (Grzegorzewski) describes large differences between people, with smoking, oral contraceptives, liver disease and medicines that use the CYP1A2 enzyme all changing caffeine levels. Because no single half-life fits everyone, we do not list one.
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