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Dr Stewart Richmond, a Research Fellow in the Department of Health Sciences at York, who led the study first reported in the Daily Mail, said: "It's a shame that these devices don't seem to have any genuine benefit.

"They're so simple and generally safe to use. But what these findings do tell us is that people who suffer with rheumatoid arthritis may be better off saving their money, or spending it on other complementary interventions, such as dietary fish oils for example, which have far better evidence for effectiveness.

"Warning people who suspect they may have rheumatoid arthritis to consult their GP and seek early medical treatment, rather than placing faith in such devices, is also important in helping to avoid long-term joint damage resulting from uncontrolled inflammation."

Dr Richmond believes that there are two main reasons why wearers sometimes report benefit: "Firstly, devices such as these provide a placebo effect for users who believe in them; secondly, people normally begin wearing them during a flare up period and then as their symptoms subside naturally over time they confuse this with a therapeutic effect.

"Pain varies greatly over time in conditions like rheumatoid arthritis, and the way we perceive pain can be altered significantly by the power of the mind".

Magnet therapy is often privately used for the management of chronic pain, with estimated worldwide annual sales of devices exceeding a billion dollars.

The practice of wearing copper bracelets to combat rheumatism has been popular since the 1970s.

An earlier study by Dr Richmond and his colleagues, published in 2009, threw doubt on the effectiveness of such devices for osteoarthritis.