Diclofenac is used to relieve pain and swelling (inflammation) from various mild to moderate painful conditions. It is used to treat muscle aches, backaches, dental pain, menstrual cramps, and sports injuries. It also reduces pain, swelling, and joint stiffness caused by arthritis. Reducing these symptoms helps you do more of your normal daily activities. This medication is known as a nonsteroidal anti-inflammatory drug (NSAID).