Aspirin. Molecular graphic of a molecule of the analgesic (painkilling) drug aspirin (acetyl- salicylic acid, C9H8O4). Atoms are shown as balls and are colour-coded: carbon (yellow), oxygen (red) and hydrogen (blue). Aspirin is a non- steroidal anti-inflammatory drug (NSAID) which blocks the production of prostaglandins in the body. Prostaglandins produce inflammation, raise body temperature and aid the perception of pain. Aspirin also has an anticoagulant action, and is used to treat patients with heart disease or those at risk from a stroke. Side-effects include erosion of the stomach lining, which may lead to a gastric ulcer.