What is naproxen? Naproxen is in a group of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs). It works by reducing hormones that cause inflammation and pain in the body. Naproxen is used to treat pain or inflammation caused by conditions such as arthritis, ankylosing spondylitis, tendinitis, bursitis, gout, or menstrual cramps. Naproxen may also be used for purposes other than those listed in this medication guide. Please consult your personal physician before taking any medication.