How long does caffeine stay in your system?

Depends: Depends on size and age of the person, and what else is in the system, but the half life is 3 to 12 hours.

Depends on dose: The more caffeine you drink, the higher the initial level. After4-6 hours your level will drop. Some of us are more sensitive, and after one cup of coffee will have effects for more than 12 hours.

Variable: In general, it is short-acting, with a half-life of about 3 hours, but there may be genetic differences as well as drug/drug and drug/food interactions. Some people are very sensitive to some effects of caffeine, and consuming some in the morning may even interfere with sleep. Drugs like caffeine alter the receptor/neurotransmitter environment, and those effects may last longer than the drug.

A long time...: It stays in your body longer than you might think. Half life of caffeine can be anywhere from three to seven hours which means it can stay in your system 5 times that long depending on your metabolism.