In humans, caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness. It is the world's most widely consumed psychoactive drug, but, unlike many other psychoactive substances, it is both legal and unregulated in nearly all parts of the world. Beverages containing caffeine, such as coffee, tea, soft drinks, and energy drinks, enjoy great popularity; in North America, 90% of adults consume caffeine daily.[5]
Caffeine is toxic at sufficiently high doses. Ordinary consumption can have low health risks, even when carried on for years – there may be a modest protective effect against some diseases, including certain types of cancer.
