This is a great question that I am frequently asked.  Before I answer, it must be pointed out that supplements are different than pharmaceuticals, or drugs.  For reasons of safety and patient’s interests, the Food and Drug Administration ( FDA ) has very stringent criteria and requirements for companies to bring a product to market.  This includes thorough investigational studies on safety and efficacy.  Supplements are considered nutraceuticals, and do not fall under the FDA requirements.  Companies can, therefore, claim many things about their products, including purity, safely, and efficacy.  There are conflicting reports on the efficacy of glucosamine at a dose of 1500 mg/day.  It appears as though chondroitin sulfate provides no benefit for the knee.