Glucosamine is a protein that is required for making other substances in the body that maintain the elasticity of tendons, muscles, and cartilage. Cartilage is necessary to ensure smooth joint movements and avoid damage to the bones in the joint. Glucosamine is commonly used as an oral supplement to treat arthritis. In a recent survey, glucosamine was ranked as the fourth most commonly used dietary supplement in this country. Diabetes (high blood sugar) is a disorder of metabolism that affects millions people in the US. There has been some concern that glucosamine supplements may raise blood sugar levels in diabetics who use it to treat their osteoarthritis. Intravenous infusions of glucosamine have been shown to alter blood sugar processing in animals, but these findings have not been confirmed in humans. There are no large, long-term studies of glucosamine use in persons with poorly controlled diabetes. Therefore, diabetics who use glucosamine to treat their arthritis should monitor their blood sugar levels frequently.