Cafeina

Caffeine is a bitter, white crystalline xanthine alkaloid that acts as a stimulant drug. Caffeine is found in varying quantities in the seeds, leaves, and fruit of some plants, where it acts as anatural pesticide that paralyzes and kills certain insects feeding on the plants. It is most commonly consumed by humans in infusions extracted from the seed of the coffee plant and the leaves of the teabush, 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, caffeineacts 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 psychoactivesubstances, 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.[4]
Caffeine is toxic at sufficiently high doses, but ordinary consumption poses few known health risks, even when carried on for years — there may be a modestprotective effect against some diseases, including certain types of cancer. Some people experience sleep disruption if they consume caffeine, especially during the evening hours, but others show littledisturbance and the effect of caffeine on sleep is highly variable.
Evidence of a risk to pregnancy is equivocal, but some authorities have concluded that prudent advice is for pregnant women tolimit consumption to the equivalent of two cups of coffee per day or less.[citation needed] Caffeine has diuretic properties when administered to people who are not used to it, but regular users developa tolerance to this effect, and studies have generally failed to support the common notion that ordinary consumption contributes significantly to dehydration. With heavy use, strong tolerance...