Time caffeine around its half-life

Caffeine’s 5–7 hour half-life means afternoon coffee is still one-quarter potency in your system at midnight.

Why it works

Caffeine is an adenosine receptor antagonist: it binds to adenosine receptors without activating them, blocking the signal that creates sleepiness. Critically, it does not eliminate adenosine — it masks its effects while adenosine continues to accumulate. When caffeine is metabolized, accumulated adenosine floods the now-unblocked receptors, producing the caffeine "crash." The half-life of 5–7 hours means a 200mg cup at 2pm leaves 50mg active at midnight for average metabolizers — enough to impair sleep architecture even if you fall asleep normally.

How to do it

1. Calculate your last caffeine cutoff: if your target sleep time is 10pm, your last caffeine (for an average metabolizer) should be before 2pm.
2. For sensitive metabolizers or those on medications that slow CYP1A2 (the caffeine-metabolizing enzyme), move the cutoff to noon.
3. Consume the majority of caffeine in the first 4 hours after waking, when adenosine pressure is lowest and caffeine’s benefit is greatest.
4. Track sleep quality for 2 weeks after shifting your caffeine cutoff — the effect is often large and immediate.

Evidence

Caffeine significantly impairs sleep quality even when consumed 6 hours before bedtime in a double-blind RCT. Individual variation in CYP1A2 metabolism is substantial. (rct)

The 5–7 hour half-life is for average metabolizers; fast metabolizers (CYP1A2 rapid) may clear caffeine in 3–4 hours; slow metabolizers may take 9–10 hours.

Sources

• Drake et al. (2013), caffeine effects on sleep taken 0, 3, or 6 hours before going to bed, Journal of Clinical Sleep Medicine

Common mistake

Judging caffeine timing by how sleepy you feel at bedtime rather than by the half-life math — caffeine impairs sleep architecture before it impairs sleep onset, so you feel fine falling asleep but sleep is lighter and less restorative.