21st Century's Double Strength Glucosamine & Chondroitin combines these two nutritional elements with a double strength serving of 1,500 mg of glucosamine and 1,200 mg of chondroitin for optimal joint support. Many scientific studies have shown the benefits of dietary supplements that combine glucosamine sulfate and chondroitin sulfate. These compounds found in the soft cartilage, tendons and synovial fluid are essential to the healthy functioning of tendons and joints, especially with advancing age.