Shark cartilage is extracted from the tough cartilage material that makes up a shark's skeleton and helps prevent compression in the joints. It is dried and powdered for marketing as a dietary supplement, often under the misleading claim that it can cure carcinoma, but this is not medically proven.
However, chondroitin sulphate, one of its most important components, has potentially positive effects on arthritis patients, and taken together with glucosamine, has become a common dietary supplement used in the treatment of osteoarthritis, where it can help to reduce pain and swelling in the joints.
Shark cartilage is reputedly an effective treatment for a specialised condition called Kaposi's sarcoma, and is also used to treat psoriasis (as a topical application), inflammation of the intestine, retinal damage due to diabetes and wound healing.
It should be noted that chondroitin sulphate can be found in the cartilage of all animals, not just sharks, and in the interests of ecology, it should also be a factor of concern that the promotion of shark cartilage supplements may be the cause of a significant decline in the shark population, so that alternative sources of animal cartilage should ethically be sought.