How long does caffeine last?

How caffeine rises and falls

Caffeine does not arrive all at once. It is absorbed from your gut over the first hour or so and peaks in your blood 30 to 120 minutes after you drink it. All but one of the 222 drinks in the Caffeine Clock database are modeled as 90 % absorbed within 35 to 45 minutes, and a drink you sip over half an hour arrives more slowly than one you finish in a minute.

Once it is in your blood, your liver breaks caffeine down at a rate proportional to how much is there. That is why caffeine fades by a half-life rather than by a fixed number of milligrams per hour: every few hours, half of what is left is gone. The caffeine half-life page explains this in more detail.

One cup of coffee, hour by hour

The table follows a 95 mg cup of drip coffee, sipped over 10 minutes at 2 pm, for three half-lives within the usual adult range. It uses the same model as the calculator above.

Even with a fast 3-hour half-life, some caffeine from an afternoon coffee is still in your body at bedtime. With a 6-hour half-life, almost half of the peak is. That is why the time of your last drink matters as much as how much you drink.

When is caffeine completely gone?

Because each half-life removes half of what is left, caffeine never drops to zero in one clean step. After five half-lives about 3 % remains, which at a 5-hour half-life is about a day. In the model, the 95 mg cup falls below 10 mg about 17 hours after you drink it and below 1 mg after about 33 hours.

For most decisions the useful question is not when caffeine is gone but when it is low enough. For sleep, the calculator starts from a 100 mg threshold, based on the European Food Safety Authority's note that 100 mg close to bedtime can affect sleep in some adults. See caffeine and sleep for how timing plays out.

Why caffeine lasts longer for some people

The 3 to 6 hours is a typical range, not a rule. About 95 % of caffeine is cleared by one liver enzyme, CYP1A2, whose activity varies five- to six-fold between people, much of it for genetic reasons.

Smoking speeds up how fast caffeine is cleared and shortens its half-life, while oral contraceptives do the opposite. Pregnancy slows clearance sharply: in one study the half-life went from an average of 3 hours in non-pregnant women to 10.5 hours in the last four weeks of pregnancy (see caffeine during pregnancy). Liver disease such as cirrhosis also slows it, and a few medicines, including the antidepressant fluvoxamine, block its breakdown.

If you know your body clears caffeine faster or slower than average, set your own half-life under Change in the calculator above and the whole curve follows it.