Caffeine and human behavior: arousal, anxiety, and performance effects.

A review of the recent literature shows the role of caffeine in the physiology, mood, and behavior of persons to be a complex one including changes in arousal, anxiety, and performance. Questions are raised as to what degree the physiological effects of caffeine are due to central nervous system stimulation and/or result from the release of catecholamines. Anxiety resulting from both high levels of caffeine (caffeinism) and caffeine withdrawal plus an association between caffeine and depression are discussed. Performance effects are mixed, with both increases and decreases reported. Effects on mental tasks are related to personality variables. The possible role of differences in initial sensitivity, adaptation to caffeine, and/or interactions with nicotine and alcohol is discussed. The present paper reviews these studies, discusses their implications for both clinical and experimental work, summarizes the major unresolved issues, and makes suggestions for new and continuing areas of research.