Drugs to prevent type 2 diabetes probably do more harm than good, according to three specialists.

They say that most patients at risk of developing the disease would be better advised to change their diets and do more exercise-interventions of proven benefit.

The warning, from specialists at the Mayo Clinic in Rochester, Minnesota, and McMaster University in Hamilton, Ontario, appear to contradict directly the results of a widely publicised study of a new drug combination, ramipril and rosiglitazone.

A trial to test this combination in people who did not have diabetes but had evidence of poor glucose control was terminated early when results showed many fewer people progressing to diabetes proper.

The Dream trial was hailed as evidence that diabetes could be prevented and the treatment, the three doctors say in British Medical Journal, is now being “aggressively marketed”.

The trial showed a 62 per cent reduction of the risk of progressing from impaired glucose tolerance to type 2 diabetes. But it also showed an increased risk of heart failure and no evidence of a fall in deaths.

Since diet and exercise changes have been shown to cut the risk of diabetes by 58 per cent, cost much less and do not have the effect of “medicalising” healthy people, they are to be preferred, says the team, led by Victor Montori, of the Mayo Clinic.

They add that it was entirely possible that the improvements found in the Dream trial were the result of rosiglitazone treating diabetes rather than preventing it. That could be proved only by discontinuing treatment and observing whether people who had been treated progressed to diabetes more slowly than they otherwise would have done. Such a trial had not yet been done.

From the patients’ point of view, it came down to the issue of whether they would prefer to take pills now in the hope of taking fewer pills later. That would be justified only if it could be shown that doing so would avoid the later complications of diabetes, which were severe.

The trials had not shown this yet. “The benefits of rosiglitazone on outcomes important to patients remain speculative,” the authors say.

The downside of taking “preventive” medicine was cost and healthy people being labelled as ill and becoming anxious as a result. “The threshold for use of drugs in otherwise healthy people must be set high,” the doctors say.

“Clinical use of glitazones to prevent diabetes is, at present, impossible to justify because of unproved benefit on patient-important outcomes or lasting effect on serum glucose, increased burden of disease labelling, serious adverse effects, increased economic burden and availability of effective, less costly lifestyle measures.”

The Dream trial, published in The Lancetin September, suggested that as many as one in 12 people should be taking rosiglitazone to prevent diabetes.

Simon O’Neill, of Diabetes UK, said: “The Medicines and Healthcare products Regulatory Agency state that rosiglitazone is a safe and effective treatment for those diagnosed with type 2 diabetes. Used as a preventative medication, the Dream study has shown that it can reduce the risk of developing the condition.”

He added, however, that Diabetes UK “strongly recommends that people at risk of developing type 2 diabetes should be incorporating increased levels of physical activity into their daily lives alongside making changes to their diet”.

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