WebMD reports that evidence suggests that glucosamine supplements are effective in counteracting deterioration of natural glucosamine levels in the body. Glucosamine may also be effective in treating joint pain from osteoarthritis, rheumatoid arthritis, inflammatory bowel disease, asthma, allergies, chronic venous insufficiency, sports injuries and chronic back pain.
WebMD explains that there is a lack of tangible evidence to show how or why glucosamine may help with these conditions, though some experts still recommend its use. High doses may cause side effects, such as upset stomach, heartburn, drowsiness and headache. Those with shellfish allergies may experience allergic reactions, but glucosamine is considered an otherwise safe supplement.