Aspirin. Molecular model of the painkilling (analgesic) drug aspirin (acetylsalicylic acid). This is a non-steroidal anti-inflammatory drug (NSAID). As well as being used as a painkiller, it is also used to help reduce fevers. It can also reduce blood clotting, and is used to treat heart attack patients and those at risk from a stroke. Its side-effects include erosion of the stomach lining, which may lead to gastric ulcers. The molecule's chemical formula is C9.H8.O4. This ball-and-stick model has colour-coded atoms: carbon (black), hydrogen (white) and oxygen (red). The double bonds in the benzene ring part of the aspirin molecule are shown in blue.