Aspirin is an anti-inflammatory drug that is widely used and prescribed as a painkiller.

Aspirin is also an anticoagulant, meaning that it has the ability to inhibit the aggregation of platelets, which are involved in coagulation and blood clotting. In healthy adults, mean bleeding time may double after a dose of aspirin. The effects of aspirin on bleeding reach their maximum within 12 hours and persist about 36 hours after the last dose of aspirin. Long-term aspirin use can lead to intestinal bleeding and stomach ulcers.

Because it works against the formation of blood clots, aspirin is sometimes proscribed for patients who have had or are at risk for having strokes.

There is currently some evidence suggesting that patients who have been prescribed aspirin as an anticoagulant have a slightly reduced risk of developing Alzheimer's disease. However, it is not known whether taking aspirin alone reduces the risk of the disease; some studies have suggested that aspirin use in healthy individuals does not affect chance of subsequently developing Alzheimer's. Given the risks of long-term anticoagulant use, most doctors do not recommend that otherwise healthy patients take aspirin to reduce risk of Alzheimer's disease.