How long does caffeine last?

Caffeine has a half-life of between three and five hours; it remains in the bloodstream for about 14 hours, according to the American Academy of Sleep Medicine. While caffeine can increase an individual's alertness, it becomes less effective with daily use.

Coffee is the source of the majority of caffeine consumed. AASM indicates that coffee and tea account for 97 percent of the caffeine used worldwide. Other sources include energy drinks, sodas, medicines and chocolate products. Caffeine is a drug and highly addictive. Withdrawal from caffeine often results in tiredness, sleepiness, a lack of energy and headaches. Too much caffeine disrupts the sleep of many individuals.