A new type of weight-loss drug may help improve risk factors for heart disease among people who are overweight, a Canadian-led research team has found.

Rimonabant, or Acomplia, is the first drug that works by blocking the cannabinoid-1 receptor, the same one marijuana targets in the brain. When the receptor is blocked in laboratory animals, they eat less and lose weight.

Jean-Pierre Després of the Quebec Heart Institute and his colleagues studied the effects of the experimental drug in 1,036 overweight or obese patients with lipid problems.

Després stressed the potential drug would not be a magic bullet for bulging waistlines, and should only be considered an option for those at high risk of diabetes and heart disease who don't respond to changes in diet and exercise.

It is "irrelevant" to people who want to lose weight for cosmetic reasons, he said.

Participants were put on a reduced-calorie diet for a month, and then randomly assigned to take a placebo, five milligrams of the drug or 20 milligrams.

Those in the placebo group lost an average of about five pounds and two centimetres off their waistlines after 12 months, compared to 19 pounds and seven to eight centimetres in the high-dose group.

Those who took the drug tended to boost their HDL or "good" cholesterol levels and reduce trigylceride levels.

Fat cell effects

The drug also increased levels of adiponectin, a protein that may help protect against diabetes and heart disease, beyond that attributed to the weight loss alone, the researchers report in the Nov. 17 issue of The New England Journal of Medicine.

Fat cells in people with bulging bellies may not produce enough adiponectin, Després said.

Side-effects of the drug included minor bouts of depression and anxiety, as well as nausea. As in many weight-loss studies, fewer than two-thirds of participants completed the trial.

A second weight-loss study on 224 obese adults found those who took the drug Meridia, generically known as sibutramine, as part of a program that includes diet therapy and physical activity lost twice as much weight as those who took only the drug.

The history of weight-loss medications like fenphen, which showed side-effects of pulmonary hypertension after it was on the market for decades, highlights the need to carefully assess the safety of antiobesity drugs, said Susan Yanovski of the National Institute of Diabetes and Digestive and Kidney Disease in a journal editorial.

While weight loss in obese people improves heart disease risk factors, "no study has yet demonstrated conclusively" that it actually reduces the risk of death or disease from heart disease, Yanovski noted.

Deprés's research was supported by Sanofi Aventis, which makes Acomplia. The drug is not being considered for approval in Canada. It may be available in the U.S. and Europe by early next year.