Cosequin Double Strength Plus MSM Joint Health Dog SupplementCosequin is a patented, scientifically researched nutritional supplement dispensed by thousands of veterinarians to help dogs maintain healthy joints. As dogs age, it is common for their joints to become less flexible which impacts their mobility and quality of life. You may have noticed that your dog has difficulty walking up stairs or jumping on the bed. While he used to be eager to play, now he is content to rest. Even at younger ages some dogs are subject to joint health concerns which affect flexibility and mobility.