Anti-addiction drugs used to treat obesity

Dramatic effects were seen from a weight loss recipe that combines anti-addiction drugs with dieting and exercise.

A group of obese trial patients put on the programme lost up to 6% of their bodyweight over the course of a year.

The study authors said the improvements were "clinically meaningful" and may reduce the risk of death.

However, the treatment's success was tempered by a lack of significant reductions in blood pressure and cholesterol levels.

US researchers recruited 1,742 patients aged 18 to 65 for the 56 week trial, but only half saw it through to the end.

Participants were randomly prescribed either a combination of the drugs naltrexone and bupropion or "dummy" placebo pills.

Naltrexone is commonly used to treat alcoholics and heroin addicts, while bupropion is better known as the anti-smoking drug Zyban. Both are known to affect appetite and reduce food cravings.

At the same time, the trial patients were given advice on lifestyle changes which included cutting down on calorie consumption and increasing exercise levels.

Patients had an average weight of around 100 kilograms (15.7 stone) at the start of the study.

Their Body Mass Index - a measurement of weight relative to height - averaged 36, classifying them as clinically obese.

The findings were reported in an online edition of The Lancet medical journal. They showed that treated participants lost between 5% and 6% of their bodyweight depending on which of two doses of naltrexone they were given. In comparison, patients in the placebo group lost 1.3%.

Those on the higher naltrexone dose shed around a stone of weight on average and a fifth lost more than 10% of their bodyweight.

The study authors, led by Professor Frank Greenway, from the Biomedical Research Centre, Louisiana State University, Baton Rouge, said weight loss of 5% to 10% had beneficial effects on the body that could reduce the risk of death.

They wrote: "Although lifestyle modification is first-line therapy for obesity, adherence to this intervention is poor.

"The combination of naltrexone plus bupropion could be a useful addition to the current range of medications that facilitate adherence to lifestyle modification and produce clinically meaningful weight loss for treatment of obesity and obesity-related disorders."

The main side effect seen was nausea, which affected more than a quarter of patients in both naltrexone dose groups.

In an accompanying article, nutrition expert Professor Arne Astrup, from the University of Copenhagen in Denmark, highlighted the lack of significant changes to blood pressure and levels of low-density lipoprotein (LDL), the "bad" form of cholesterol.

He wrote: "After 56 weeks, blood pressure was not reduced as much as would normally be seen with a five kilogram weight loss, and the reduction was less than that in the placebo group. Additionally, the combination treatment did not reduce LDL cholesterol more than did placebo.

"More data are needed to get a better overall assessment of cardiovascular (heart and arteries) risk of this otherwise promising combination therapy for obesity."