Caffeine
C₈H₁₀N₄O₂·194.191 g/mol·Pharmaceutical·CID 2519
StimulantCommon
The world's most widely consumed psychoactive substance. A purine alkaloid that blocks adenosine receptors, promoting wakefulness. Found in coffee (~95 mg/cup), tea (~45 mg/cup), and chocolate. Half-life ~5 hours in humans.