Why is the medical community disapproving of glucosamine chondroitin supplements?

Lack of evidence: There is no hard conclusive evidence that they work. Anecdotes do not count. However, if the diagnosis is osteoarthritis, especially of the knee or shoulder, i usually have patients give glucosamine a three month trial as glucosamine is very safe (unless shellfish allergy). If it does work, it works within three months. Less problems than with prescription medications.