Many people take glucosamine and chondroitin supplements for arthritis pain, but a controlled trial has found no evidence that the combination works. In fact, in this study, the placebo worked better.

Spanish researchers randomized 164 men and women with knee osteoarthritis to take a single daily dose of 1,500 milligrams of glucosamine and 1,200 of chondroitin, or an identical looking placebo. The study is in Arthritis & Rheumatology.

The researchers used a scale that shows 10 faces with increasingly pained expressions and asks patients which picture matches their degree of pain. People who took the medicines had a 19 percent reduction in pain scores after six months on the regimen. But those who took the placebo had a 33 percent reduction.

On scales measuring how well the knee worked, there was no difference between the treatment and control groups.