When will your caffeine peak and wear off?
Caffeine blocks adenosine receptors in the brain, preventing the drowsiness signal. It peaks in blood plasma at 30-60 minutes after consumption and has a half-life of 5 hours in average adults (range: 3-7 hours). This means 200mg at 2 PM leaves ~100mg at 7 PM and ~50mg at midnight — enough to disrupt sleep quality. The FDA considers 400mg/day safe for most adults (roughly 4 cups of brewed coffee). Sensitivity varies widely based on genetics (CYP1A2 enzyme variants), age, medications, and liver function. Caffeine tolerance develops in 7-12 days of regular use. Withdrawal symptoms (headache, fatigue, irritability) begin 12-24 hours after last dose and peak at 20-51 hours. Pregnant women should limit intake to 200mg/day. Coffee drinkers metabolize caffeine faster than non-regular consumers.