Caffeine is a psychoactive drug that exerts a powerful stimulant effect on the central nervous system. It is naturally found in coffee, tea, and chocolate, but is also added to some soft drinks (e.g. colas), energy drinks and energy shots.[1] The National Health and Nutrition Examination Survey (NHANES) found that roughly 89% of adults in the US consume caffeine daily.[2] People often use caffeine-containing beverages to help restore alertness and wakefulness or to reduce drowsiness when feeling mentally fatigued.[3][4] Caffeine is also available as a purified powder, and it is found in some dietary supplements claiming to cause weight loss or increase energy (e.g. pre-workouts).[1][5][6] Additionally, caffeine is found in some over-the-counter drugs used to relieve pain[7][8] and in prescription drugs used to treat breathing problems in premature babies.[9]
After ingestion, caffeine acts rapidly on the central nervous system, triggering several short-lived effects including an increase in heart rate, blood pressure, and urine output.[10][11][12][13] However, with regular daily use, these symptoms of caffeine typically become less pronounced.[10][12][1][3][4]