☕ Caffeine and Sleep

How caffeine works

Caffeine blocks adenosine, a chemical that builds up throughout the day and makes you feel sleepy. By blocking its receptors, caffeine tricks your brain into thinking it's not tired. But the adenosine is still accumulating — when the caffeine wears off, you feel the full impact.

Half-life: 5-6 hours

Caffeine's half-life means that half the caffeine from a 3 PM coffee is still in your system at 9 PM. A quarter is still there at 3 AM. This varies by person — some metabolize it faster, others slower.

Recommendations

• Set a personal caffeine cutoff — 2 PM is a safe bet for most people
• Remember that tea, chocolate, cola, and energy drinks also contain caffeine
• If you're sensitive, even decaf has small amounts (2-15 mg per cup)
• Caffeine doesn't replace sleep — it only masks tiredness temporarily

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