Some people wear copper bracelets or magnetic wrist straps to treat arthritis pain.

But a study from the University of York says they have no effect.

"It appears that any perceived benefit obtained from wearing a magnetic or copper bracelet can be attributed to psychological placebo effects," researcher Stewart Richmond said. "People tend to buy them when they are in a lot of pain, then when the pain eases off over time, they attribute this to the device. However, our findings suggest that such devices have no real advantage over placebo wrist straps that are not magnetic and do not contain copper."

The study was a randomized trial on 45 people with osteoarthritis. Each wore four devices in a random order over a 16-week period. They wore two wrist straps with differing levels of magnetism, a demagnetized wrist strap and a copper bracelet.

"Although their use is generally harmless, people with osteoarthritis should be especially cautious about spending large sums of money on magnet therapy. Magnets removed from disused speakers are much cheaper, but you would first have to believe that they could work," Richmond said.

The study revealed no meaningful difference between the devices in terms of their effects on pain, stiffness and physical function, a news release said.

The research was published in the journal Complementary Therapies in Medicine.