Glucosamine is a natural compound in your body that helps make your cartilage strong and rigid. In Europe, glucosamine is a prescription drug with a standardized formula. In the United States and some parts of Asia, glucosamine is sold over the counter as a dietary supplement.
Many people regularly take glucosamine to protect cartilage, as well as to help manage osteoarthritis pain. In theory, some of the glucosamine in dietary supplements makes its way from your digestive tract to damaged joints, where it reinforces worn cartilage. But research has never demonstrated this effect.
Studies randomly assigning people with knee arthritis to two or three years of treatment with glucosamine or placebo have found that the rate of cartilage loss — measured as narrowing of space in the knee joint on X-rays over time — has been about the same in both groups.
Some experts consider glucosamine supplements harmless. If you're already being treated for arthritis, though, talk to your doctor before you take glucosamine or any other dietary supplement.