Injectable hyaluronic acid is used in the treatment of mild to moderate osteoarthritis (OA) of the knee. It is injected directly into the knee in a series of three or four injections one week apart. Not everyone on this therapy obtains relief, but those who do usually experience pain relief for up to six months. Hyaluronic acid has also been added to oral combination supplements, but to date there is no evidence that it improves the effectiveness of glucosamine or chondroitin. Oral hyaluronic acid is digested in the gastrointestinal tract and poses no known risks to the patient.