Osteoarthritis is a disabling affliction expected to increase in the coming decades, and disease- modifying osteoarthritis drugs (DMOADs) would be highly desirable adjuncts to symptomatic relief and structure reconstruction as they may delay the disease process. Chondroitin sulfate and glucosamine have been observed to exert beneficial effects on the metabolism of various cells involved in osteoarthritis as well as in animal models and clinical trials. Clinical trials have reported beneficial effects of both these biological agents, alone or in combination, on pain and functions as well as their structure-modifying capacity reported and analyzed in recent meta-analyses. Nonetheless, the effectiveness of these bioactive (macro)molecules as DMOADs reported from randomized trials is mismatched. Current studies with varying levels of evidence suggest that chondroitin sulfate and glucosamine can modify the disease progression but at the same time there are not absolute certainties on their efficacy in modifying the course of the disease. This comprehensive review aims to clarify the role of these compounds in the therapeutic molecules/ drugs useful to patients affected by osteoarthritis.