NOW Extra Strength Glucosamine & Chondroitin combines two well-known joint support ingredients in their sulfate forms.* Glucosamine is an essential building block for the formation of glycosaminoglycans (GAGs) and proteoglycans, the main components of cartilage tissue.* Chondroitin sulfate is a glycosaminoglycan that has been combined with glucosamine in this product for the support of proper joint mobility and comfort.* This extra strength product has twice the glucosamine/chondroitin (750 mg/600 mg per tablet) as in our regular strength product (375 mg/300 mg per capsule). NOW Foods developed the glucosamine test method chosen as the official AOACI industry standard method.