Aspirin. Molecular graphic of a molecule of the analgesic (painkilling) drug aspirin (acetylsali- cylic acid, C9.H8.O4). Atoms are shown as balls and are colour-coded: carbon (yellow), hydrogen (blue) and oxygen (red). A map of electrostatic potential surrounds the molecule. Aspirin is a non-steroidal anti-inflammatory drug (NSAID) which 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.