Swiss researchers combined results from recent large-scale studies on chondroitin's effectiveness. They found that people taking chondroitin had no better improvement in joint health or pain relief than those taking the placebo.

"The longer you look and the more rigorously you look, the less effect you see," said Dr. Peter J¨¹nii, an epidemiologist at Switzerland's University of Bern and an author of the new study. "We shouldn't expect that this is a magic bullet - it isn't."

This review came after another recent study that looked at chondroitin in conjunction with different supplement, glucosamine. The two are frequently sold in combination.

The study found neither chondroitin nor glucosamine alone, nor the two in combination were better than a placebo for arthritis pain.

As to why many patients swear by chondroitin as a treatment, J¨¹ni suggested that osteoarthritis -- the degenerative joint disease seen especially in older people -- is a condition that does not progress invariably toward more severe symptoms.

Chondroitin, a cartilage extract, is sold across America in health food stores, pharmacies and online. It is often combined with glucosamine, an amino sugar. Experts estimate that U.S. sales of chondroitin-glucosamine supplements now top 1 billion U.S. dollars per year.