Glucosamine is extracted from a material (chitin) present in the shells of crabs, oysters, and shrimp. Glucosamine is taken in tablet or capsule form, usually as glucosamine sulfate, but sometimes as glucosamine hydrochloride. Glucosamine often is taken with chondroitin sulfate (see Chondroitin Sulfate).
People take glucosamine mostly to treat osteoarthritis of the knee. Its role in treating osteoarthritis in other locations is less well defined. Evidence is conflicting. Some evidence suggests it has both pain-relieving and disease-modifying effects, whereas other large and well-designed studies show it to be of no benefit. One very large study has shown that glucosamine hydrochloride is beneficial only when combined with chondroitin sulfate.
Glucosamine is safe for most people. Common side effects are itching and mild digestive problems such as heartburn, diarrhea, vomiting, and nausea. People who have a shellfish allergy and take glucosamine extracted from shellfish may have an allergic reaction. Glucosamine may increase blood sugar in people with diabetes. Reports say that glucosamine increases the effects of warfarin (a drug that prevents blood clots) and thus increases the risk of bleeding. It may also reduce the effectiveness of such drugs as acetaminophen and some drugs that treat cancer and diabetes.