Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class.[12] It is mainly used recreationally, as a eugeroic (wakefulness promoter) or as a mild cognitive enhancer to increase alertness and attentional performance.[13][14] Caffeine acts by blocking binding of adenosine to the adenosine A1 receptor, which enhances release of the neurotransmitter acetylcholine.[15] Caffeine has a three-dimensional structure similar to that of adenosine, which allows it to bind and block its receptors.[16] Caffeine also increases cyclic AMP levels through nonselective inhibition of phosphodiesterase.[17]
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