A new study suggests that two popular dietary supplements for arthritis pain do almost nothing to alleviate the aches in patients' knees.

While there's a chance some patients might be helped, the study found no overall benefit from either glucosamine or chondroitin, said Dr. Chester Oddis, a professor in the division of rheumatology and clinical immunology at the University of Pittsburgh School of Medicine.

He was principal investigator for the local part of the national study, whose findings were published today in the New England Journal of Medicine.

Dietary supplement companies, including Pittsburgh-based GNC Corp., hoped glucosamine and chondroitin would be the next big products for an industry that has lost several top sellers in recent years and is struggling to grow. Even yesterday, the Couhcil for Responsible Nutrition, a trade group, stressed the positive by calling for more research to determine the full potential of the supplements for arthritis patients.

But Gary M. Giblen, an analyst who follows the supplement industry for Brean Murray, Carret in New York, said the study, which elaborates on disappointing results released in November, throws cold water on the hopes of investors.

"There was a lot of promise that this would be a powerful catalyst, but it was not to be," Mr. Giblen said.

Nutrition Business Journal, a trade publication in San Diego, estimated U.S. sales of glucosamine and chondroitin at $750 million last year.

Dr. Oddis said the supplements likely will remain popular with some patients, in part because they appear safer than certain pain-relieving medications.

Last year, the U.S. Food and Drug Administration directed that Motrin, Advil, Naprosyn, Aleve and Celebrex -- also known as ibuprofen, naproxen and celecoxib -- carry warnings for potential increased risk of heart attack, stroke or gastrointestinal bleeding.

The painkillers Vioxx and Bextra were pulled from the market in recent years because of their potential for health risks. Both are so-called Cox-2 inhibitors, which are gentler on the stomach than older pain relievers.

Osteoarthritis, a chronic condition involving the breakdown of a joint's cartilage, affects at least 20 million Americans, and the number is expected to double in the next two decades as the baby boom generation ages.

The wear and tear of aging is believed to be a risk factor along with obesity, injury or heredity. Weight loss and exercise may help, though patients eventually may need joint replacement.

Glucosamine is a form of amino sugar that may play a role in cartilage formation and repair, according to the Arthritis Foundation. Chondroitin is believed to give cartilage elasticity.

Both are sold widely as nutritional supplements, but whether the supplements help arthritis patients is poorly understood, Dr. Daniel Clegg, of the University of Utah School of Medicine and the study's principal investigator, said yesterday in a conference call with reporters.

The study randomly assigned 1,583 patients with knee osteoarthritis to receive either glucosamine hydrochloride, chondroitin sulfate, both supplements together, Celebrex, or a placebo for 24 weeks.

"Overall, glucosamine and chondroitin sulfate were not significantly better than a placebo in reducing knee pain," the study found.

A subgroup of patients with moderate to severe knee pain did show a benefit from taking both supplements, but researchers said the findings need to be confirmed by other studies.

The results are unlikely to change the minds of many doctors and patients about the supplements, said Dr. Kelly Krohn, director of clinical research in Mercy Hospital's medicine department.

Dr. Elliot Goldberg, a rheumatologist and director of medical education at the Western Pennsylvania Hospital, said he doesn't recommend the supplements but sees no harm in taking them.

Dr. Krohn said he has recommended them for years and "this study did not dissuade me from continuing to do that."

Particularly interesting, he said, is a later study planned for a subgroup of patients aimed at assessing whether the two supplements slow damage to cartilage. Dr. Clegg said researchers hope to have results at the end of the year.

Glucosamine and chondroitin are just the latest in a series of new products that have failed to generate a significant buzz for supplement companies, said Mr. Giblen, the industry analyst. Lacking big new products, companies can do little more than slash prices to compete, which hurts the bottom line, he said.

"They've been questing for the holy grail since the late 1990s -- for the next hot product," he said. "And there haven't been any."