RESEARCH · 1997
Coffee plus a short nap beat coffee alone
Reyner LA, Horne JA. Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology. 1997;34(6):721–725.
At a glance
- Who
- 12 sleepy adults
- Setup
- A 30-minute break, then a two-hour monotonous afternoon drive in a car simulator
- Compared
- 200 mg of caffeine followed by a nap of under 15 minutes, 200 mg of caffeine only, and a placebo
- Finding
- Coffee plus a nap cut driving incidents to 9% of the placebo level. Caffeine alone: 34%.
What they did
After their 1996 study showed that a short nap and caffeine each help for about an hour, Louise Reyner and Jim Horne tried the two together, and over a longer drive. Before a two-hour afternoon drive in a simulator, volunteers had a 30-minute break in which they either took 200 mg of caffeine and then napped for under 15 minutes, took the caffeine without a nap, or had a placebo.
What they found
- With the placebo, driving incidents, felt sleepiness and the brain signs of drowsiness all showed the familiar mid-afternoon peak.
- Caffeine alone reduced that peak. Caffeine plus a nap made it disappear.
- Driving incidents fell to 9% of the placebo level with the combination, against 34% with caffeine alone.
- Naps that were only "non-sleep dozing", resting without really falling asleep, still worked.
What it means for your coffee nap
This is the core evidence for the coffee nap: caffeine first, then a nap of up to 15–20 minutes. It also means you don't have to worry if you don't fall properly asleep. Lie down, close your eyes, and get up with the alarm.
Limits
Twelve volunteers in a driving simulator. And a coffee nap is a short-term boost: if you're exhausted at the wheel, the safe choice is still to stop driving.