Why can late-afternoon coffee at your destination sabotage first-night jet lag?

Answer: Caffeine lingers for hours

Caffeine lingers for hours ✓ — Caffeine has a long enough half-life that a useful afternoon rescue can still be active near bedtime. CDC travel guidance gives caffeine a roughly 5-hour half-life and advises avoiding stimulants before bed. The trap is that coffee solves the local-afternoon meeting while quietly borrowing from the local-night recovery window.

It instantly resets sleep — Coffee can help alertness, but it is not an instant sleep reset. CDC traveler guidance treats caffeine as a daytime alertness tool and tells travelers to avoid it in the evening. The difference matters: alertness can rise while the underlying clock mismatch and next bedtime problem remain.

It wears off quickly — Many people feel coffee "wear off" after the obvious buzz fades, but pharmacology is slower than sensation. A mean half-life near 5 hours means a meaningful fraction can remain into bedtime. The bedtime problem is not whether you still feel wired; it is that enough stimulant may remain to push wakefulness.