Supplements taken by millions of arthritis sufferers worldwide do not work, experts have said.
Glucosamine and chondroitin are frequently used to try to alleviate pain from osteoarthritis, which mostly occurs in the knees, hips and small joints. This is the most common type of arthritis in the UK, with an estimated 8.5 million sufferers.
Now experts have carried out a study which shows the supplements do not work, although they said patients will not suffer harm if they take them.
The research was published online in the British Medical Journal (BMJ).
According to the Department of Health, one type of glucosamine is available on NHS prescription for arthritis, alongside chondroitin. Glucosamine comes in two types - glucosamine hydrochloride which can be prescribed on the NHS and glucosamine sulphate which can be bought as a supplement.
The National Institute for Health and Clinical Excellence (Nice) has said neither supplement - in any form - is backed by evidence.
The review of 10 existing studies found the supplements were not effective when taken alone or in combination.
More than 3,800 patients suffering from osteoarthritis in their hips, knees or both joints took part in the studies. Patients were typically aged 58 to 66 and had suffered symptoms for between six months and 10 years.
However, the authors, led by Professor Peter Juni at the University of Bern in Switzerland, said some patients did think the supplements helped them.
"We are confident that neither of the preparations is dangerous," the authors said. "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."