How long does caffeine stay in your system?

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.