MODEL RELEASED. Aspirin. Silhouette of an elderly woman taking an aspirin pill. Aspirin is a mild pain killer, or analgesic, used to relieve headache, menstrual pain and muscle discomfort. Other uses include controlling fever and decreasing the risk of stroke or heart attack by reducing blood clotting. Aspirin is the common name for acetylsalicylic acid. It works by decreasing the production of pain transmitting chemicals called prostaglandins that can cause pain, swelling and fever.