Glucosamine is one of the most popular dietary supplements sold in the United States. Most clinical trials have focused on its use in osteoarthritis of the knee. The reported adverse effects have been relatively well studied and are generally uncommon and minor. No significant supplement-drug interactions involving glucosamine have been reported. The National Institutes of Health-sponsored Glucosamine/chondroitin Arthritis Intervention Trial, the largest randomized, double-blind, placebo-controlled study involving the supplement, still has not confirmed whether glucosamine is effective in the treatment of osteoarthritis. Despite conflicting results in studies, there is no clear evidence to recommend against its use. If physicians have patients who wish to try glucosamine, it would be reasonable to support a 60-day trial of glucosamine sulfate, especially in those at high risk of secondary effects from other accepted treatments. The decision to continue therapy can then be left to patients on an individual basis, while the physician monitors for possible adverse effects. Glucosamine should be used with caution in patients who have shellfish allergies or asthma, and in those taking diabetes medications or warfarin.