Glucosamine is the most commonly used chondroprotective supplement for the treatment of osteoarthritis. Chondroitin is the second most commonly used supplement for the treatment of osteoarthritis. Glucosamine is an aminosugar that is incorporated into joint cartilage. It is supplied as a supplement in one of three forms: glucosamine sulfate, glucosamine hydrochloride, or N-acetylglucosamine. Studies show that while all three forms of glucosamine are effective, glucosamine hydrochloride and glucosamine sulfate were more effective than N-acetylglucosamine. Glucosamine is rapidly taken up by cartilage cells and help stimulate the synthesis of joint fluid and cartilage and also helps inhibit the destructive enzymes that can destroy cartilage and proteoglycans. The anti-inflammatory aspect of glucosamine may result from the scavenging of harmful free radicals similar to antioxidants. Glucosamine is used by the cartilage for the synthesis of glycosaminoglycans.

A number of studies in people and pets show that glucosamine is equally effective for treating osteoarthritis when compared to NSAIDs, and without the side effects.

While a number of glucosamine products are available from reputable manufacturers, many of the early major studies done in pets have used a proprietary product (Cosequin and Cosequin-DS) containing glucosamine and chondroitin. Clinical evidence indicates other products from well-known manufacturers are also effective.