Supplements. Many over-the-counter nutrition supplements have been used for treatment of OA. Most lack good research data to support their effectiveness and safety. Among the most widely used are glucosamine/chondroitin sulfate, calcium and vitamin D, and omega-3 fatty acids. To ensure safety and avoid drug interactions, consult your doctor or pharmacist before using any of these supplements. This is especially true when you are combining these supplements with prescribed drugs.