With more than 100 years of use, aspirin is one of the most extensively studied drugs in the history of medicine. In addition to its analgesic, anti-inflammatory, and antipyretic effects, acetylsalicylic acid is a potent irreversible inhibitor of platelet aggregation. In the late 19th century the acetylation of salicylic acid in an attempt to make it less bitter and hence more palatable inadvertently gave this compound a unique property—the acetyl group can be transferred to the serine residue in the active site of the enzyme cyclooxygenase (COX), irreversibly inhibiting its function and thereby preventing the production of prostaglandins.
Gaziano JM, Greenland P. When Should Aspirin Be Used for Prevention of Cardiovascular Events?. JAMA. 2014;312(23):2503-2504. doi:10.1001/jama.2014.16047