From the Manufacturer:
Only CosaminDS contains researched 95% pure low molecular weight chondroitin sulfate selected by the National Institutes of Health (NIH) for a major clinical study.
Only CosaminDS contains researched high purity chondroitin sulfate allowing you to maintain your comfort level at a lower intake of tablets.
Because other supplements use inferior, unproven grades of glucosamine or chondroitin sulfate, this research can be applied only to CosaminDS.