Patients with osteoarthritis of the knee who were treated with high-quality, prescription-grade chondroitin got as much pain relief after six months as those treated with a nonsteroidal anti-inflammatory drug, a new clinical trial has found. They also showed similar improvements in function, such as the ability to walk distances and perform daily activities.

As part of the trial, 604 patients with knee arthritis received either the NSAID drug celecoxib (brand name Celebrex, 200 milligrams a day), a dummy pill, or chondroitin (800 milligrams a day), a component of cartilage that cushions the joints and is sold as a dietary supplement in the United States. Those on chondroitin or the NSAID fared better than those treated with a placebo, though it took longer for chondroitin to work.

The study, published in Annals of the Rheumatic Diseases, was sponsored by IBSA Institut Biochimique SA, a Swiss drug company that markets the chondroitin formulation. The researchers say the trial protocol adhered to European regulatory guidelines for testing osteoarthritis drugs.

Previous studies of chondroitin have shown mixed results. The author of the study, Jean-Yves Reginster, a professor of public health, epidemiology and health economics at Liege State University in Belgium, said the difference may be the formulation, since pharmaceutical-grade chondroitin is not available in the United States. The results obtained with one particular formulation “cannot be extrapolated to over-the-counter or generic products,” Dr. Reginster said.