Relafen^® (nabumetone) is a presciption medication that has been licensed to relieve symptoms of osteoarthritis and rheumatoid arthritis. Relafen is not a cure for these types of arthritis, nor does it slow the progression of the disease. Part of a class of drugs called nonsteroidal anti-inflammatory drugs (NSAIDs), Relafen is also used to treat several other conditions related to pain, inflammation, swelling, and stiffness. Relafen comes in the form of a tablet that is taken by mouth. Its side effects can include swelling, unexplained rash, and constipation.