A combo pill of two addiction drugs can help people lose weight, say US researchers.
Naltrexone, commonly used to treat alcoholics and heroin addicts, and the anti-smoking drug bupropion led to greater weight loss than diet and exercise alone, reports The Lancet.
It is thought the treatment may help beat food cravings.
Professor Nick Finer, an obesity expert from University College London (UCL), said the drug might prove more useful if researchers can better identify who would benefit.
In the study, 1,700 overweight and obese adults were all offered a weight-loss programme with diet and exercise advice.
Two-thirds were also given the combination treatment (in one of two doses) and a third were given a placebo, or dummy pill, to take twice a day.
Only half completed the trial, which lasted a year.
Overall those taking the treatment lost an average of 5pct to 6pct of their weight depending on the dose, compared with 1.3pct in the placebo group.
The researchers said if only those who completed the trial were included, weight loss was 8pct of body weight for those on the anti-addiction drugs.
The treatment also had side effects including nausea, headaches, constipation, dizziness, vomiting and a dry mouth.
The drug is designed to target both the parts of the brain controlling appetite but also reward.
Regulators in the US are currently looking at whether the treatment, which will be marketed as Contrave, should be licensed.
Study leader Professor Frank Greenway, from Pennington Biomedical Research Center in Louisiana, said although 5pct may not seem like a huge weight loss, it could make a real difference in terms of health risks.
"I think the weight loss we saw was significant even if it might not be as much as many people would like to see," the BBC quoted him as saying.
"This is the first drug I'm aware of that targets both the appetite and reward centres in the brain.
"People who struggle with cravings seem to have better control with their eating. In practice it is likely to be used in people who feel cravings get in the way of their ability to lose weight," he added.