You had coffee at 3 PM and now its midnight and your staring at the ceiling. Caffeine stays in your body longer than most people realize.
The Half-Life: 5-6 Hours
Caffeines half-life is about 5-6 hours for most adults. That means if you drink 200mg of caffeine at noon, you still have 100mg in your system at 5-6 PM, and 50mg at 10-11 PM.
It takes roughly 10-12 hours for caffeine to fully clear your system.
Why Some People Process Caffeine Faster
Caffeine metabolism varies significently between individuals:
- Genetics: Some people have genes that break down caffeine quickly. Others are slow metabolizers.
- Smoking: Smokers metabolize caffeine almost twice as fast.
- Pregnancy: Caffeine half-life can extend to 9-11 hours.
- Birth control: Oral contraceptives slow caffeine metabolism.
- Liver function: Liver health affects how quickly you process caffeine.
How Much Caffeine Is In Your Cup
Typical caffeine amounts:
- 8 oz drip coffee: 95-200mg
- 8 oz cold brew: 100-200mg
- Double espresso: 125mg
- 8 oz black tea: 40-70mg
- 12 oz cola: 35-45mg
- Energy drink: 80-300mg
When Caffeine Stops Affecting You
You stop feeling caffeine long before it leaves your system. The alertness fades after 3-4 hours, but the caffeine still effects your sleep quality even if you dont feel wired.
Why Afternoon Coffee Hurts Sleep
Even if you fall asleep fine, caffeine in your system reduces deep sleep. You sleep lighter, wake up more often, and feel less rested. Studies show coffee 6 hours before bed can reduce sleep quality by over 1 hour.
The Safe Cutoff
For most people, stopping caffeine 8-10 hours before bed allows enough time to clear your system. If you go to bed at 10 PM:
- Safe: Last coffee at noon-2 PM
- Risky: Coffee after 2 PM
- Sleep-killer: Coffee after 4 PM
Testing Your Sensitivity
Not sure how caffeine effects you? Try cutting it off at noon for two weeks. If your sleep improves, your more sensative than you thought. If nothing changes, you might be a fast metabolizer who can handle afternoon coffee.