Aspirin. Molecular model of the drug aspirin, also known as acetylsalicylic acid (C9.H8.O4). This drug is used as an analgesic (painkiller), an anti-pyretic (fever reducer) and as an anti-inflammatory. It can also reduce blood clotting, and is used to treat heart attack patients and those at risk from a stroke. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white) and oxygen (red).