Expired aspirin is aspirin that is past the expiration date printed on the container. According to Bayer Healthcare LLC, using aspirin or any over-the-counter drug past the expiration date is not recommended as its effectiveness may be diminished.
Bayer Healthcare LLC explains that aspirin relieves pain by reducing hormone-like substances in the body known as prostaglandins. Prostaglandins are produced in tissues in the body in response to trauma or injury and are part of a system that relays feelings of pain, redness and swelling and fever in the body.
Aspirin also reduces the presence of substances involved in blood clotting, says Bayer Healthcare LLC. For this reason, some physicians recommend some individuals take aspirin to reduce the likelihood of recurrent heart attack or ischemic stroke.