Aspirin (acetylsalicylic acid, ASA), one of the class of medications referred to as non-steroidal anti-inflammatory drugs (NSAIDs), is available over-the-counter and by prescription, in a variety of preparations. It is an “analgesic,” which refers to drug or medicine that reduces pain without rendering the person taking it unconscious. Acetylsalicylic acid is a derivative of salicylic acid, originally developed over 100 years ago from a substance called salicin found in the bark and leaves of willow plants. It works by inhibiting the production of prostaglandins, which are chemicals produced by the body to sensitize it to pain. It is effective in reducing fever, pain, swelling and blood clots. Consequently, acetylsalicylic acid is used to treat a wide variety of conditions, including systemic lupus erythematosus. Aspirin is a registered trademark owned by Bayer, the company that originally developed ASA. Over the years the term Aspirin has come to be used interchangeably with acetylsalicylic acid and ASA.