What changes how fast you clear caffeine

How your body clears caffeine

Caffeine is broken down mainly in the liver by the enzyme CYP1A2. Anything that changes that enzyme's activity changes your half-life.

Factors that can change it

• Genetics: variants affecting CYP1A2 make some people faster and others slower.
• Smoking: regular smoking is linked with faster clearance.
• Pregnancy: clearance slows markedly as pregnancy progresses.
• Hormonal contraceptives, liver conditions and some medicines: these can slow clearance.
• Age: newborns clear caffeine very slowly. Evidence for changes in later life is mixed, and age alone predicts clearance poorly.

How the calculator reflects this

Choose fast (about 3 hours), normal (about 5) or slow (about 8) in the caffeine metabolism calculator, and tick Pregnant or Smoker if they apply. The tool cannot measure your metabolism, so the choice is yours. See what half-life means for the basics.

If you take medication or have a health condition, ask a doctor or pharmacist how it may interact with caffeine.