Chondroitin sulfate is a sulfated glycosaminoglycan (GAG) composed of a chain of alternating sugars (N-acetylgalactosamine and glucuronic acid). It is usually found attached to proteins as part of a proteoglycan. A chondroitin chain can have over 100 individual sugars, each of which can be sulfated in variable positions and quantities. Understanding the functions of such diversity in chondroitin sulfate and related glycosaminoglycans is a major goal of glycobiology. Chondroitin sulfate is an important structural component of cartilage and provides much of its resistance to compression . Along with glucosamine, chondroitin sulfate has become a widely used dietary supplement for treatment of osteoarthritis.

Chondroitin is an ingredient found commonly in dietary supplements used as an alternative medicine to treat osteoarthritis and also approved and regulated as a symptomatic slow-acting drug for this disease (SYSADOA) in Europe and some other countries. It is commonly sold together with glucosamine. Chondroitin and glucosamine are also used in veterinary medicine.

While Chondroitin sulfate is a prescription or over-the-counter drug in 22 countries, chondroitin is regulated in the U.S. as a dietary supplement by the Food and Drug Administration. As a result, in chondroitin sulfate supplements, there are no mandatory standards for formulation, and no guarantee that the product is correctly labelled. This is not the case of Europe where there is a chondroitin sulfate formulation approved as a drug and considered as the reference product, with evidenced efficacy and safety demonstrated by clinical trials in osteoarthritic patients. Adebowale et al. reported in 2000 that of 32 chondroitin supplements they analysed, only 5 were labeled correctly, and more than half contained less than 40% of the labeled amount. Hence, the importance of testing the bioequivalence of all chondroitin sulfate formulations with the reference product approved in Europe. However, United States Pharmacopoeia  testing standards now exist for the identification and quantification of chondroitin.
The dosage of oral chondroitin used in human clinical trials is 800–1,200 mg per day. Most chondroitin appears to be made from extracts of cartilaginous cow and pig tissues , but other sources  Since chondroitin is not a uniform substance, and is naturally present in a wide variety of forms, the precise composition of each supplement will vary.[5] In fact, although many food supplement companies produce their products in compliance with human food processing GMP  , most of them do not produce their products in compliance with the GMP regulations for pharmaceuticals, resulting in products without pharmaceutical requirements.Recent testing has revealed several flaws in the older testing methods. Without knowing the source of the chondroitin  and the approximate age of the animal, it is impossible to get a reliable reference standard and thus results from previous testing had yielded percentages between 50-400%.