Glucosamine XL supports healthy cartilage and joint function and contains (per 1 measure):  4,635 mg glucosamine sulfate.  Glucosamine is one of the most common ingredients in horse joint supplements. Not only is it a precursor for chondroitin sulfate and other glycosaminoglycans (GAGs) found in articular cartilage, research suggests its protective role in joints goes beyond supplying the basic building blocks for the production of new, healthy tissue. Scientists now believe glucosamine has the ability to block enzymes and mediators that lead to cartilage breakdown.