Coffee nap: how it works and how to time it
A coffee nap is a coffee followed at once by a 15 to 20 minute nap. It sounds backwards, and it works better than either one alone.
In a driving-simulator study, sleepy drivers who took caffeine and then napped had 9 percent as many incidents as drivers given a placebo. Caffeine on its own brought the figure to 34 percent.
Why does a coffee nap work?
Caffeine is not instant. It is absorbed over the first half hour and peaks at around 45 minutes. A short nap fits inside that gap.
The two also act on the same thing. Sleepiness comes from adenosine, which builds up while you are awake. A nap clears some of it. Caffeine blocks the receptors that the rest would act on. You wake with less adenosine and with caffeine arriving at the same moment.
How to take a coffee nap
- Drink it fast. The clock starts when you finish. An espresso or a small cold coffee is easier to finish in a couple of minutes than a hot mug.
- Lie down at once. Set an alarm for 20 minutes.
- Do not worry about falling asleep. In the driving study, naps where people only dozed without sleeping properly still worked.
- Get up when the alarm goes. Past 20 minutes you start to enter deep sleep, and waking from it leaves you groggier than before.
- Add light. In a second study, bright light straight after a short nap helped as well. Step outside or open the blinds.
How much caffeine for a coffee nap?
Both studies used 200 mg, taken in one go. That is about two mugs of filter coffee, three single espressos, or a can of Celsius.
Smaller doses were not tested in those studies. But 200 mg at lunchtime is a lot of caffeine if you also want to sleep that night:
| Dose | Taken at | Still active at 11 pm | For sleep |
|---|---|---|---|
| 200 mg | 1 pm | 61 mg | still above it |
| 200 mg | 3 pm | 77 mg | still above it |
| 100 mg | 1 pm | 30 mg | below the line |
| 100 mg | 3 pm | 39 mg | below the line |
One mug, around 100 mg, is the version that fits an ordinary day. It gives up some of the effect measured in the studies and keeps the night.
When is the best time for a coffee nap?
Early afternoon, between 1 pm and 3 pm. That is when the natural dip in alertness falls, and it is early enough for a small dose to clear by bedtime.
After 3 pm, skip the coffee and keep the nap. A 20 minute nap on its own still helps, and it costs nothing at night. The cutoff for your own bedtime gives the exact hour.
Does a coffee nap ruin sleep at night?
That depends on the dose and the hour, and the studies did not measure it. They tested alertness in the hour or two after the nap, not sleep that night.
By the model this site uses, 200 mg at 1 pm is still above the sleep line at 11 pm. A review of 24 studies points the same way: it puts the cutoff for about 217 mg at more than thirteen hours before bed. If you take the full dose, treat it as a morning tool.
A coffee nap borrows alertness from the evening. With one mug before 3 pm the loan is small. With 200 mg at 4 pm you pay for it at midnight.
Who should use a coffee nap?
Drivers on a long trip. This is what the method was tested for. Pull over somewhere safe, drink, nap, and drive on. It buys an hour or two. It does not replace a night's sleep, and if you are still sleepy afterwards, stop driving.
Shift workers before a night shift, where the sleep that follows is in the daytime anyway.
Anyone facing a long afternoon after a short night, as an occasional fix.
It is a poor daily habit. If you need one every afternoon, the problem is the night before, and the likeliest cause is caffeine taken too late the previous day.
Sources
- Reyner LA, Horne JA. Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology, 1997.
- Hayashi M, Masuda A, Hori T. The alerting effects of caffeine, bright light and face washing after a short daytime nap. Clinical Neurophysiology, 2003.
- Gardiner C, Weakley J, Burke LM, and others. The effect of caffeine on subsequent sleep: a systematic review and meta-analysis. Sleep Medicine Reviews, 2023.
Common questions
What is a coffee nap?
You drink a coffee quickly and lie down straight away for 15 to 20 minutes. The caffeine takes effect as you wake, so you get the benefit of the nap and the coffee together.
Do coffee naps actually work?
In two controlled studies, yes. In a driving simulator, caffeine followed by a nap of under 15 minutes cut driving incidents to 9 percent of the level seen with a placebo. Caffeine alone cut them to 34 percent.
How long should a coffee nap be?
15 to 20 minutes. Longer than that and you are likely to wake from deep sleep feeling groggy, which cancels the benefit.
Will a coffee nap ruin my sleep at night?
It can. The studies used 200 mg, which taken at 1 pm still leaves about 61 mg active at 11 pm by this site's model. One mug of about 100 mg before 3 pm is the safer version.
