Caffeine is a bitter, white crystalline xanthine alkaloid.. Caffeine is found in varying quantities in the seeds, leaves, beans and fruit of some plants, where it acts as a natural pesticide that paralyzes and kills certain insects feeding on the plants, as well as enhancing the reward memory of pollinators. It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the tea bush, as well as from various foods and drinks containing products derived from the kola nut. Other sources include yerba maté, guarana berries, guayusa, and the yaupon holly.
In humans, caffeine acts as a central nervous system stimulant, temporarily warding off drowsiness and restoring alertness. . Beverages containing caffeine, such as coffee, tea, soft drinks, and energy drinks, enjoy great popularity. In North America, 90% of adults consume caffeine daily.
Part of the reason caffeine is classified by the Food and Drug Administration as GRAS (generally recognized as safe) is that toxic doses (over 10 grams) are much higher than typically used doses (less than 500 milligrams). Ordinary consumption can have low health risks, even when carried on for years – .