How fast caffeine kicks in
Caffeine is absorbed quickly. About 99% of it is absorbed within 45 minutes, and the level in the blood peaks 15 to 120 minutes after drinking, according to the Institute of Medicine's review of caffeine pharmacology. The model behind the tables on this page puts the peak about 1 hour 50 minutes after the drink, toward the slow end of that range.
The half-life of caffeine
A half-life is the time it takes to clear half of what is there. For caffeine it is about 5 hours in the average adult (StatPearls), and it ranges from 1.5 to 9.5 hours between healthy people (Institute of Medicine). Each half-life removes half of what is left, so the amount falls fast at first and slowly later.
This is a 95 mg cup of coffee, about an 8 oz cup of brewed coffee, at a fast, a typical and a slow half-life. Times count from when you have the drink.
| Half-life | 1 h | 2 h | 4 h | 6 h | 8 h | 12 h | 24 h |
|---|---|---|---|---|---|---|---|
| 3 hours | 62 mg | 65 mg | 45 mg | 28 mg | 18 mg | 7 mg | 0 mg |
| 5 hours | 66 mg | 73 mg | 60 mg | 46 mg | 35 mg | 20 mg | 4 mg |
| 8 hours | 68 mg | 79 mg | 71 mg | 60 mg | 51 mg | 36 mg | 13 mg |
At a typical 5-hour half-life, the cup is down to 46 mg after 6 hours, 20 mg after 12 and 4 mg after a full day. At 8 hours, 36 mg is still there after 12 hours.
Caffeine left after each hour, by drink
The same curve for common drinks, at a 5-hour half-life. Serving sizes and caffeine amounts are the defaults in the WaterChamp app.
| Drink | Caffeine | After 2 h | After 4 h | After 6 h | After 8 h | After 10 h | After 12 h |
|---|---|---|---|---|---|---|---|
| Cold Brew | 200 mg | 155 mg | 127 mg | 97 mg | 73 mg | 56 mg | 42 mg |
| Drip Coffee | 140 mg | 108 mg | 89 mg | 68 mg | 51 mg | 39 mg | 29 mg |
| Black Coffee | 95 mg | 73 mg | 60 mg | 46 mg | 35 mg | 26 mg | 20 mg |
| Energy Drink | 80 mg | 62 mg | 51 mg | 39 mg | 29 mg | 22 mg | 17 mg |
| Espresso | 63 mg | 49 mg | 40 mg | 30 mg | 23 mg | 17 mg | 13 mg |
| Matcha Latte | 70 mg | 54 mg | 44 mg | 34 mg | 26 mg | 19 mg | 15 mg |
| Black Tea | 47 mg | 36 mg | 30 mg | 23 mg | 17 mg | 13 mg | 10 mg |
| Cola | 33 mg | 25 mg | 21 mg | 16 mg | 12 mg | 9 mg | 7 mg |
| Green Tea | 30 mg | 23 mg | 19 mg | 15 mg | 11 mg | 8 mg | 6 mg |
A 200 mg cold brew at 2 pm still leaves 73 mg at 10 pm, more than a whole cup of black tea holds. A 33 mg cola at the same time leaves 12 mg.
What makes caffeine last longer
Most caffeine is broken down in the liver by one enzyme, CYP1A2, which handles about 95% of it. How fast that happens differs with age, sex and hormones, liver disease, obesity, smoking and diet (Nehlig, 2018).
- Smoking speeds up caffeine clearance (Institute of Medicine).
- Birth control pills can double the half-life (Institute of Medicine).
- Pregnancy slows clearance. In one study the average half-life was 8.3 hours in pregnant women, and up to 16 hours in some, against 3.4 hours in men and in women who were not pregnant (Knutti, 1981).
The FDA notes wide variation both in how sensitive people are to caffeine and in how fast they eliminate it (FDA). If you do not know your own rate, compare the 3, 5 and 8 hour rows in the first table.
Can you clear caffeine faster?
No. None of the sources above describe a way to speed it up, and drinking water or exercising is not among the factors that change the liver's rate. To bring the level down, stop adding caffeine and wait.
Energy drinks follow the same curve
An energy drink lasts as long as a coffee with the same amount of caffeine. A 250 ml can with 80 mg leaves about 39 mg after 6 hours and 22 mg after 10. Larger cans hold more, so check the label, or see the energy drink page.
Caffeine and sleep
In a sleep study, 400 mg of caffeine taken 6 hours before bed still disrupted sleep, and the authors advise against substantial caffeine for at least 6 hours before bedtime (Drake, 2013). The sleep monitor recorded more than an hour less total sleep, and the 12 participants did not report the loss themselves (AASM). Smaller doses count too: the European Food Safety Authority says a single 100 mg dose may affect sleep in some adults, particularly close to bedtime (EFSA).
To see how much caffeine is left at your own bedtime, and the latest time for one more cup, add your drinks to the caffeine calculator.
Questions
How long does it take for caffeine to wear off?
At a 5-hour half-life, about half of a coffee is gone after 5 hours and about three quarters after 10. A 95 mg cup drops below 10 mg after about 17 hours.
How long does caffeine take to kick in?
Most of it is absorbed within 45 minutes, and the level peaks 15 to 120 minutes after you drink (Institute of Medicine).
How long does an energy drink last?
As long as a coffee with the same caffeine. A 250 ml can with 80 mg still leaves about 39 mg after 6 hours and 22 mg after 10, at a 5-hour half-life.
When should I stop drinking coffee before bed?
The sleep study above supports at least 6 hours. For one 95 mg coffee, an 11 pm bedtime and a 70 kg (154 lb) adult, the caffeine calculator puts the latest start near 4 pm at a 5-hour half-life.
