ISOTONIX OPC-3 90 Servings for 3 months 10.6oz by Isotonix opc Isotonix OPC-3 is an isotonic-capable food supplement that is made from a combination of bilberry, grape seed, red wine and pine bark extracts, and citrus extract bioflavonoids, all found to be powerful antioxidants. Oligomeric proanthocyanidins (OPCs) are bioflavonoids (complex organic plant compounds) found in fruits, vegetables and certain tree barks that provide exceptional nutritional benefits to the human body. Studies have shown OPCs to be up to 20 times more powerful than vitamin C.