Claims that diet drug rimonabant (Acomplia / Zimulti) offers benefits beyond those associated with weight loss may not be justified, according to a new report by independent British medical experts.

The diet drug has been sold as Acomplia in the U.K. since June 2006 for treatment of obese and some overweight adults, and developer Sanofi Aventis has claimed some of the improvement in cardiometabolic risk factors observed in clinical trials cannot solely be attributed to weight loss.

Cardiometabolic risk factors -- including low HDL (good) cholesterol, high LDL (bad) cholesterol, elevated fat levels in the blood, high blood pressure and insulin resistance -- in combination increase a person's chance of developing heart disease and/or type 2 diabetes.

The drug "has a beneficial effect on blood glucose and lipid levels -- a more beneficial effect than would be expected from weight loss alone," Sanofi claims on its website.

But experts writing in the Drug and Therapeutics Bulletin (DTB), published by the British Medical Journal (BMJ) on May 30th, said there was no proof in the clinical trials that the drug had any beneficial effects outside those expected by weight loss.

"It might be related to increased activity based on the lifestyle advice given to participants at the start of the trials," according to their report. "Furthermore, it is not known whether rimonabant's effects on individual risk factors translate into a reduced long-term likelihood of cardiovascular events."

The experts said the trials also showed rimonabant to have no effect on LDL cholesterol and little or no effect on high blood pressure.

While the drug is available in the U.K., the country's National Institute for Health and Clinical Excellence (Nice) is still weighing whether and under what conditions the drug should be paid for by the National Health Service.

"Rimonabant has not been directly compared with other, less expensive, drug treatments for obesity. Also, as with these other treatments, it is not known whether rimonabant reduces the likelihood of obesity-related diseases, such as cardiovascular problems," the researchers concluded.

They said Xenical (orlistat) "is the drug for obesity for which there is the most evidence for efficacy and safety to date, and we have previously concluded that it is a reasonable option for obese patients where diet and exercise and/or behavioural measures alone have failed.

"On current evidence, we do not believe that rimonabant represents a significant advance for patients with obesity," they said.