Cherie Blair is a fan - and now they're available on the NHS. But Jeremy Laurance wonders whether magnets really can treat everything from period pains to backache and insomnia

Professional sceptics of alternative medicine got their comeuppance last week with the disclosure that magnet therapy, said to be favoured by Cherie Blair, was to be made available on the NHS. Magnets have been used as a remedy for centuries, and widely marketed in Britain for over a decade, but this was a seal of scientific approval.

You can buy a magnetic hairbrush said to stimulate hair growth, a magnetic mask to reduce wrinkles, magnetic insoles to boost energy, and magnetic jewellery to ward off arthritis. Some researchers claim to have shown that magnets can ease period pains, lift depression and cure aching joints. Separate studies at Harvard University, in the US, and the Peninsula Medical School, Plymouth, even found that wearing a magnetic sleeve eased the pain of osteoarthritis of the knee.

Magnets' healing powers are said to have enthused Cleopatra, and current users are reported to include Bill Clinton and Sir Anthony Hopkins. But when the NHS includes a product in the Drug Tariff, you have to sit up and take notice. Since last week, a device called the 4UlcerCare - a strap containing four magnets that is wrapped around the leg - has been available on prescription from GPs. Its maker, the Bristol-based firm Magnopulse, claims that it speeds the healing of leg ulcers and prevents their recurrence.

The announcement has created excitement in the world of alternative medicine. Every purveyor of magnetic devices has been pumping out press releases and advertisements, hoping to capitalise on the new development. Lilias Curtin, one-time therapist to Cherie Blair, sent a poster-sized announcement to newspapers last week declaring her "sincere belief that, in the next five to 10 years, magnets will be seen in first-aid boxes". Kleshna, a maker of magnet jewellery, claimed in another release that magnets created "a whirlpool effect to the iron in our blood to get it pumping round much faster than usual".

People may scoff at the idea that the lumps of metal used for sticking notes on to the fridge have healing properties, but, presumably, those who control the NHS purse know what they are paying for. And anyone who doubts that magnets have physical effects on the body need only try an experiment conducted at the Institute of Neurology in London. Ask Professor Tom Rothwell to wave a magnetic wand over the left side of your head, and watch your right arm jump involuntarily. The excitation of the neuronal pathways that this demonstrates suggests, according to Professor Rothwell, that the technique might be useful in the rehabilitation of stroke victims. A trial of transmagnetic stimulation of the brain in stroke-sufferers is soon to begin.

This does not prove that magnetic necklaces have medicinal effects. But after 10 years of making and selling magnetic devices such as the 4Ulcer-Care leg wrap, Derek Price, the 64-year-old founder of Magno-pulse, is convinced that they work. Having had initial success on his dog, Kiri, who suffered from arthritis; and then on his own arthritic ankle, Price sent the leg wraps to four local surgeries to be tried on patients. To his surprise, word came back that they were helping to heal ulcers. A trial was run on 28 patients in Suffolk, Norfolk and Cambridge by the London GP Nyjon Eccles, and the results published in the Journal of Wound Care in February 2005. A second telephone survey found that 211 of 289 patients who used the device had not had a recurrence of their ulcer for at least a year, Price says.

Whether this was what convinced the NHS Prescription Pricing Authority to include it in the Drug Tariff is hard to tell. No one was available from the authority to comment last week, and a spokesman for the Department of Health could throw no light on what evidence is required before a product can be included in the Drug Tariff. "It is for the GP to decide whether a listed product is suitable for the treatment of individual patients," he said.

The leg-ulcer wrap is worn just below the knee, above the calf muscle. It does not come into direct contact with the ulcer, which is covered by its own dressing. It is believed that the magnets stimulate the circulation but it is not known how. Leg ulcers tend to occur in the elderly and those with poor circulation such as diabetics. Their treatment costs the NHS at least £300m a year. The cost to the NHS of the leg-ulcer wrap is £13.80 - about half the retail price of £29 - and Price claims that it could save £150m a year on conventional treatment and nurses' time.

Other experts are sceptical. Professor Edzard Ernst, head of complementary medicine at the University of Exeter, said that he was puzzled by the NHS decision. "As far as I can see, there hasn't yet been enough research to prove that these magnets help people with ulcers. You need more than a study on 20-odd people to have a compelling case."

More powerful electromagnets could help to heal tissue injuries, and are used in hospitals elsewhere in Europe, but that was different, he said. His own study of small magnets on arthritis sufferers had failed to yield compelling results. "There is a huge market out there and lots of money is being made, but the evidence is far from convincing."

In January, researchers from the Kaiser Permanente Medical Center, in California, published a paper in the British Medical Journal that cast doubt on the therapeutic use of magnets. "Patients should be advised that magnet therapy has no proven benefits. If they insist on using a magnetic device, they could be advised to buy the cheapest - this will alleviate the pain in their wallet," they wrote.

That could be good advice for the NHS.

Jeremy Laurance is health editor of 'The Independent'

Magnets: do they really work?

* The origins of magnet therapy can be traced back to ancient Egypt, but they became popular in the West in the 1990s. Around five million Americans were using magnets in 2001.

* Magnets are said to help with arthritis, aches and pains, circulation problems, migraine, backache, period pain and sleep problems.

* Magnets used for therapy are the size of a 50p piece and eight-10 times stronger than fridge magnets.

* At the University of Virginia, in the US, researchers concluded that magnet therapy reduced the intensity of pain from fibromyalgia - a rheumatoid disorder - enough to be "clinically meaningful".

* At Harvard University, patients with osteoarthritis were given magnetic "sleeves" for their knees, which they wore six hours a day for six weeks. The researchers found that the beneficial effects kicked in after four hours, with a sevenfold difference between those who had the magnetic sleeve and those who had a sham device.

* For a study at the University of Washington, researchers put a magnet on the shoulder of patients who had suffered chronic pain for years. After the magnet had been on the shoulder for one hour, pain levels halved.

* A study published in the British Medical Journal in January concluded that there was no evidence that magnet therapy worked, and warned magnet users that they were being exploited.