Naproxen is used for:

Treating rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, and juvenile arthritis. It is used to treat tendonitis, bursitis, gout, menstrual cramps, or mild to moderate pain. It may also be used for other conditions as determined by your doctor.

Naproxen is an NSAID. Exactly how it works is not known. It may block certain substances in the body that are linked to inflammation. NSAIDs treat the symptoms of pain and inflammation. They do not treat the disease that causes those symptoms...