How Long Does Caffeine Last?
Quick Answer
Caffeine's half-life is 5-6 hours in most adults. That means half remains in your system 5-6 hours after consumption. Full effects peak at 30-60 minutes and last 3-5 hours. Sleep disruption can occur if consumed within 6-8 hours of bedtime. Genetics significantly affect how fast you metabolize caffeine.
Key Points
- 5-6 hour half-life in most adults
- Peak effects at 30-60 minutes
- Genetics cause 2-4x variation between people
- Can impair sleep even when you don't feel alert
- Last coffee by 2pm for most people
Detailed Answer
Caffeine pharmacokinetics vary widely between people, but here's the typical timeline:
• 0-15 minutes: Absorption begins • 30-60 minutes: Peak blood levels and maximum alertness • 3-5 hours: Most noticeable effects wear off • 5-6 hours: Half-life (50% still in system) • 10-12 hours: 75% eliminated • 24+ hours: Complete elimination
Factors that slow caffeine metabolism:
• Genetics: CYP1A2 gene variants ("slow metabolizers") can double half-life • Pregnancy: Half-life increases to 10-20 hours • Oral contraceptives: Doubles half-life in some women • Liver disease: Significantly impairs clearance • Age: Elderly metabolize caffeine more slowly
Factors that speed it up:
• Smoking: Increases metabolism by 50% • High cruciferous vegetable intake • Regular caffeine use (partial tolerance)
Sleep implications: Caffeine blocks adenosine receptors. Even after you stop feeling alert, it can impair deep sleep architecture. The 2pm cutoff rule exists for good reason.
Evidence Quality
Multiple high-quality studies support this
Key Sources:
- reviewCaffeine Pharmacokinetics: Clinical Review
- studyCYP1A2 Polymorphisms and Caffeine Metabolism
- reviewCaffeine and Sleep Quality: Meta-Analysis
Related Questions
Genetics. If you're a "slow metabolizer" (CYP1A2 gene variant), caffeine lingers longer. About 40% of people are slow metabolizers. You probably know if you are based on past experience.
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