Caffeine
About Caffeine
Caffeine is a methylxanthine stimulant and the most widely consumed psychoactive substance in the world, found in coffee, tea, cocoa, cola and energy drinks. It acts mainly by blocking adenosine A1 and A2A receptors, counteracting the drowsiness promoting effects of adenosine. It is absorbed rapidly and broken down in the liver mainly by CYP1A2, whose activity varies with genetics, smoking, pregnancy and oral contraceptive use, so the duration of its effects differs widely between people. Caffeine improves alertness, reaction time and vigilance and enhances athletic performance, particularly in endurance events. Regular use leads to tolerance, and stopping abruptly can cause headache, fatigue, irritability and poor concentration for several days. The FDA has described a daily intake not generally associated with harm in healthy adults, and lower limits are advised in pregnancy, when high intake has been linked to miscarriage. Very high doses, especially from concentrated powders, can cause palpitations, anxiety and potentially fatal toxicity.
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