Caffeine
The world's most popular stimulant — and one of the most common hidden causes of poor sleep. Understanding its half-life is the key to enjoying it without wrecking your night.
- Common cutoff: 8–10 hours before bed
- Evidence strength: Strong — it clearly disrupts sleep
How caffeine works
Throughout the day, a molecule called adenosine builds up in your brain and makes you feel sleepy — it's part of your natural sleep pressure. Caffeine works by blocking adenosine's receptors, so you don't feel that sleepiness. The catch: the adenosine is still there, waiting. When caffeine wears off, it can hit all at once.
The half-life problem
Caffeine's 'half-life' — the time for your body to clear half of it — is roughly five to six hours, but it varies enormously between people based on genetics, age, and other factors. That means a 2 p.m. coffee can still have a meaningful amount of caffeine circulating at 8 p.m., quietly reducing your deep sleep even if you fall asleep fine.
Finding your cutoff
Because of that long half-life, a caffeine cutoff of eight to ten hours before bed is a sensible default for most people — earlier if you're sensitive. The exact right time depends on your bedtime and your personal sensitivity.
References
- Drake C, et al. Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed. J Clin Sleep Med. 2013.
- Clark I, Landolt HP. Coffee, caffeine, and sleep. Sleep Med Rev. 2017.
Caffeine: FAQ
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