“In the first study, glucosamine sulfate was given to healthy volunteers in doses of 750, 1500, or 3000 mg once daily. In the second study, oral glucosamine sulfate capsules (1500 mg) were given daily for two weeks to 12 people with osteoarthritis. Glucosamine concentrations in plasma and synovial fluid increased significantly from baseline levels […] but the levels are still ten- to a hundredfold lower than required to positively affect the cartilage (chondrocytes) to build new tissue”

⇒ the good news is that these molecules make it through the intestines intact, and arrive at the place where they are supposed to help. The bad news seems to be you would need to take huge doses.