Two supplements taken by millions of people for joint pain caused by arthritis do not work, according to research.
The supplements, glucosamine and chondroitin, are widely sold in health shops and have increasingly been prescribed by GPs and rheumatologosts in the last decade.
They are taken on their own or in combination to reduce the pain caused by arthritis in the hips and knees. In 2008 the global market for glucosamine alone was estimated at £1.3bn.
But analysis of results from 10 trials of the supplements involving over 3,800 patients with knee and hip osteoarthritis found they were no better than a placebo at relieving pain.
Osteoarthritis is a chronic condition of the hip or knee which can cause severe long-lasting pain. The main treatment is painkillers and anti-inflammatory drugs to reduce the swelling in the joints.
However the drugs cause stomach and heart problems in some people, especially if used long term. There is an urgent need for treatments that slow the disease and relieve pain, the researchers say.
Writing in the British Medical Journal, Professor Peter Juni and colleagues at the University of Bern, Switzerland, say conflicting results from trials about the effectiveness of the two supplements led them to carry out the review. They found no clinically relevant effect either on joint pain or on joint space narrowing – a measure of the damage caused by osteoarthritis.
Osteoarthritis is the most common type of arthritis in the UK, affecting an estimated 8.5 million people. It is thought to be caused by mechanical failure of the cartilage that separates and cushions the joints.
The other main type, rheumatoid arthritis, is caused by inflammation of the lining of the joints and the sheaths around the tendons.
Professor Juni and colleagues say that in the absence of any evidence that the supplements work, they should not be paid for by health services.
"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."
Some patients find the supplements beneficial but the authors suggest this is either because of the placebo effect, or due to the natural course of the illness.
They conclude: "We are confident that neither of the preparations is dangerous. Therefore, we see no harm in having patients continue these preparations as long as they perceive a benefit and cover the costs of treatment themselves."