Aspirin tablets and blisterpack packaging. Aspirin (acetylsalicylic acid) is an analgesic (pain relieving) drug. It is a non-prescription drug and is used to relieve general pain such as headaches. Aspirin is also used to thin the blood, which reduces the risk of blood clots that can cause heart attacks and strokes. Aspirin was first sold as a medicinal drug by the German pharmaceutical company Bayer, following Felix Hoffman's synthesis of aspirin in 1897.