Coffee after lunch ruins my sleep but not my friend's

You are likely a slow caffeine metaboliser, and the CYP1A2 gene keeps caffeine active in your body for up to ten hours instead of four.

Why it happens

If you carry the slow variant, a 2pm coffee can still be circulating at midnight, while your friend with the fast variant cleared the same cup by dinner. Same drink, opposite night. Around half of all adults are slow metabolisers, so this is extremely common.

One thing to try

Cut all caffeine after noon for one week. If you fall asleep noticeably faster, you have your answer about your own wiring.

Each decode is a research-backed tendency, not a diagnosis. A tap tells you how your body is likely wired and what to try, it does not label you, and nothing here is a substitute for a doctor where a medical question is involved.