A combination pill of two drugs used to treat addiction may help people lose weight, say US researchers.
The Lancet reports that 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.
It is thought the treatment may help beat food cravings.
However, one UK expert said he would like to see much higher weight loss for the drug to be used in clinics.
Professor Nick Finer, an obesity expert from University College London (UCL), said the drug may prove more useful if researchers can better identify who would benefit.
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This is the first drug I’m aware of that targets both the appetite and reward centres in the brain”
Professor Frank Greenway
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 5% to 6% of their weight depending on the dose, compared with 1.3% in the placebo group.
The researchers said if only those who completed the trial were included, weight loss was 8% of body weight for those on the anti-addiction drugs.
The treatment was not without side effects which included 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 5% 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,” he said.
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He said a separate trial of the same drug but with a more intensive diet and exercise programme had shown a 10% average weight loss, compared with 5% in the placebo group.
“This is the first drug I’m aware of that targets both the appetite and reward centres in the brain,” he said.
“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.”
Professor Finer, from UCL, said combination treatments were likely to be the future for obesity drugs.
But he said he was not overly impressed with the weight loss seen in the trial, especially given the side-effects.
“The question will be can they define who the responders are and also can you get better results by combining the drug with a more effective weight loss programme,” he said.
“We desperately need effective drugs but we have to have very high standards of safety and acceptability to patients.”