Diclofenac is a medicine that reduces swelling (inflammation) and pain. It's used to treat aches and pains, as well as problems with joints, muscles and bones. These include: rheumatoid arthritis and osteoarthritis, sprains and strains in muscles and ligaments, back pain,toothache, migraine, gout, ankylosing spondylitis – this causes inflammation of the spine and other parts of the body.