Two popular supplements taken by millions of people around the world to combat joint pain, do not work, finds research published online in the British Medical Journal.

The supplements, glucosamine and chondroitin, are either taken on their own or in combination to reduce the pain caused by osteoarthritis in hips and knees.

The researchers, led by Professor Peter Jüni at the University of Bern in Switzerland, argue that given these supplements are not dangerous "we see no harm in having patients continue these preparations as long as they perceive a benefit and cover the cost of treatment themselves."

However, they add: "Health authorities and health insurers should not cover the costs for these preparations, and new prescriptions to patients who have not received treatment should be discouraged."

Osteoarthritis of the hip or knee is a chronic condition which is mainly treated with painkillers and anti-inflammatory drugs but these can cause stomach and heart problems, especially if used long-term. Treatments that not only reduce pain but slow the progression of the disease would be desirable, say the authors.

In the last decade, GPs and rheumatologists have increasingly prescribed glucosamine and chondroitin to their patients. And many individuals around the world have purchased them over the counter. In 2008 global sales of glucosamine supplements reached almost $2bn, which represents an increase of about 60% since 2003.

The authors say that results from existing trials about the effectiveness of glucosamine and chondroitin are conflicting. A large scale review of studies was therefore needed to determine whether or not the supplements work.

Professor Jüni and colleagues analysed the results of 10 published trials involving 3,803 patients with knee or hip osteoarthritis. They assessed changes in levels of pain after patients took glucosamine, chondroitin, or their combination with placebo or head to head.

They found no clinically relevant effect of chondroitin, glucosamine, or their combination on perceived joint pain or on joint space narrowing.

Despite this finding, some patients are convinced that these preparations are beneficial, say the authors. They suggest this might be because of the natural course of osteoarthritis or the placebo effect.

"Compared with placebo, glucosamine, chondroitin, and their combination do not reduce joint pain or have an impact on narrowing of joint space. Health authorities and health insurers should be discouraged from funding glucosamine and chondroitin treatment," they conclude.