Q. I read that a recent study found glucosamine hydrochloride was ineffective for arthritis knee pain. But what about glucosamine sulfate?

A. Timothy E. McAlindon, MD, MPH, chief of the Division of Rheumatology and professor at Tufts School of Medicine, responds: Its controversial. Most biochemists I know assert that there really isnt any difference between the hydrochloride and sulfated versions because they dissociate in the stomach. The manufacturer of glucosamine sulfate claims otherwise, but I have never heard a satisfactory explanation of why that should be the case. There are clinical trials of glucosamine sulfate, but they were all performed by the manufacturer, with close involvement in performance of the statistical analyses and writing of the manuscripts. Most reviewers downgrade the weight of evidence from those studies because of industry bias.