Indomethacin is used to relieve moderate to severe pain, tenderness, swelling, and stiffness caused by osteoarthritis (arthritis caused by a breakdown of the lining of the joints), rheumatoid arthritis (arthritis caused by swelling of the lining of the joints), and ankylosing spondylitis (arthritis that mainly affects the spine). Indomethacin is also used to treat pain in the shoulder caused by bursitis (inflammation of a fluid-filled sac in the shoulder joint) and tendinitis (inflammation of the tissue that connects muscle to bone). Indomethacin is in a class of medications called NSAIDs. It works by stopping the bodys production of a substance that causes pain, fever, and inflammation.