Diclofenac is a nonsteroidal anti-inflammatory drug (NSAID). This medicine works by reducing substances in the body that cause pain and inflammation. Diclofenac is used to treat pain or inflammation caused by arthritis or ankylosing spondylitis. Diclofenac powder (Cambia) is used to treat a migraine headache attack. Do not use this medication to treat a cluster headache. Cambia will only treat a headache that has already begun. It will not prevent headaches or reduce the number of attacks. Diclofenac may also be used for purposes not listed in this medication guide.