Life & Career · 咖啡因（Caffeine） · Updated 2026-10-25
What Is Caffeine?
Definition
Typical caffeine loads: a medium Americano 150-200 mg, latte 75-100 mg, tea 30-50 mg, cola 35 mg, energy drinks 80-160 mg. Half-life runs ~5 hours (3-7 by CYP1A2 genotype): 200 mg at 16:00 leaves 100 mg at 21:00 and 50 mg at 2 a.m. — enough to erode deep sleep. Caps: 400 mg/day for healthy adults, 200 mg in pregnancy, 100 mg for teens. Tolerance builds in 1-2 weeks; withdrawal headaches last 2-9 days.
Formula
Remaining = dose × 0.5^(hours elapsed / 5)
Worked Example
A 300 mg Americano at 18:00 leaves 150 mg at 23:00 and 75 mg at 4 a.m. — the "wired at midnight" effect. Moving it before noon protects a 23:00 bedtime.
Common Misconception
"Coffee dehydrates you" — at normal intake it is net water-positive per cup. And "tea is caffeine-light" — equal-weight tea leaves beat coffee beans; strong tea ≈ half a coffee. Caffeine sobers no one — it only masks intoxication while blood alcohol stays high.
Matching Calculators
Related Terms
Keep Exploring
Browse the full glossary, or head back to the homepage for 1,435 free online calculators.
Back to glossary