Glucosamine is a chemical that is made naturally in the human body. It mostly pools as fluid around the joints, which helps explain why it is taken to help in joint pain, as it serves to increase the lubricative fluid around joints and bones. For supplements, glucosamine is also often extracted from the shells of shellfish like oysters, crabs, and shrimp. However, not all glucosamine supplements are from natural sources – some are synthetically created in laboratories.