Psychophysiological Aspects of Caffeine Consumption

Caffeine may be the psychoactive compound most widely used in the United States. Caffeine appears in coffee, tea, cola drinks, chocolate bars and cocoa, cold and diet medications, and sleep-prevention compounds; the amount of caffeine varies in different substances and according to preparations. Research on caffeine's effects on alcoholic drinks, alertness, anxiety, heart rate, performance, and sleep is reviewed. Caffeine is usually not harmful, although long-range effects of caffeine have not been thoroughly investigated. Caffeine's effects often have been studied by means of ingestion of coffee but substances other than caffeine may be active in coffee and tea. The placebo effect contributes to some of the effects experienced by coffee-caffeine users.