Caffeine

Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class and is the most commonly consumed psychoactive drug globally. It is mainly used for its eugeroic, ergogenic, or nootropic (cognitive-enhancing) properties ; it is also used recreationally, often in social settings. Caffeine acts by blocking the binding of adenosine at a number of adenosine receptor types, inhibiting t... (Wikipedia)