Aspirin. Computer graphic of a molecule of the painkilling (analgesic) drug aspirin (C9.H8.O4, acetylsalicylic acid). Atoms (balls) are connected by sticks (bonds). The balls are colour-coded: carbon (brown), hydrogen (white) and oxygen (red). Aspirin, a non-steroidal anti-inflammatory drug (NSAID), blocks the production of prostaglandins in the body. Prostaglandins control inflammation, body temperature and the perception of pain. Aspirin also has an anticoagulant action, and is used to treat heart disease patients and those at risk from a stroke. Side effects include stomach lining erosion, which may lead to a gastric ulcer.