Glucosamine and chondroitin, two animal products marketed as food supplements, do appear to help relieve symptoms of osteoarthritis. The authors analyzed 15 previously published studies of the effects of glucosamine and chondroitin on osteoarthritis. The combined results of the studies, adjusted for quality and variability in the supplements, indicated a moderate benefit from glucosamine treatment and a large benefit from chondroitin treatment.
However, the researchers uncovered some quality problems with previous research which suggest that the actual benefit of treatment with glucosamine and chondroitin is likely to be less than the studies indicate.
The Journal of the American Medical Association March 15, 2000;283:1469-1475, 1483-1484
The reason why this study is so important is that it was published in the biggest medical journal in the world, JAMA. When JAMA reports that an alternative therapy works, you had better believe that it works as they only reluctantly publish findings which promote natural therapies. Glucosamine and chondortin do work.
However, it is important that one use high quality products. There is no question that these cartilage precursors do work for osteoarthritis (not rheumatoid arthritis). The likely explanation for some of the conflicting previously published research likely has to do with the quality of the supplements that were used.