The largest and longest study of the obesity drug Wegovy has shown people maintain significant weight loss for at least four years, with fewer serious adverse events than those given placebo 'dummy' treatment.
Doctors say the finding will add pressure on UK health authorities, which currently limit treatment to just two years.
Results revealed at an international obesity conference show those given weekly injections of the drug shed pounds for the first 65 weeks of treatment, and then sustained a stable body weight over the longer term.
On average they lost 10.2% of their body weight and 7.7cm from their waist size after four years.
Significantly, even those who were only slightly obese, or who only lost a small amount of weight, still benefited from a reduction in cardiovascular risks, according to results presented at the European Congress on Obesity in Venice and published in the journal Nature Medicine.
Dr Simon Cork, senior lecturer in physiology at Anglia Ruskin University, who wasn't involved in the study, said the results show for the first time that patients maintain a "weight plateau" if they continue treatment long term.
"Importantly one of the decisions by the UK health service to limit (treatment) to two years was because of questionable long-term cost effectiveness," he said.
He added: "That this data demonstrates improved cardiovascular and metabolic parameters continuing to four years may go some way to negating that argument.
"This study also neatly demonstrates that obesity is a lifelong condition and the decision by NICE to limit prescription to two years does a disservice to patients suffering with obesity."
The SELECT (Semaglutide and Cardiovascular Outcomes) trial involved 17,604 adults with obesity or who were overweight from 41 countries. None of them had diabetes, but all had previously had a heart attack, stroke or peripheral artery disease.
Over the first two years of the study, the proportion of people who were obese fell sharply from 71% to 43% in the group given Wegovy.
But in those given placebo injections, the rate dropped only slightly, from 72% to 68%.
After three years of treatment, participants had a 20% lower risk of a heart attack, stroke or dying from cardiovascular disease, according to analysis released last year.
Professor Donna Ryan from Pennington Biomedical Research Centre in New Orleans, USA, who led the study, said the weight loss was seen irrespective of age, gender and ethnicity.
"This degree of weight loss in such a large and diverse population suggests that it may be possible to impact the public health burden of multiple obesity-related illnesses," she said.
"While our trial focused on cardiovascular events, many other chronic diseases including several types of cancer, osteoarthritis, and anxiety and depression would benefit from effective weight management."
The study showed that serious adverse events were less common in those given the drug than those given placebo.
That was largely because people taking Wegovy were less likely to have cardiac disorders.
But people taking the drug were more likely to have gallbladder stones, and were more likely to stop taking treatment because of gastrointestinal problems such as nausea and diarrhoea.
A second analysis of the same group of patients, led by UK researchers, showed that cardiovascular benefits were seen even in patients who only had mild obesity or lost only modest amounts of weight.
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Tap hereProfessor John Deanfield, from University College London, said the finding had "important" clinical implications.
"Around half of the patients that I see in my cardiovascular practice have levels of weight equivalent to those in the SELECT trial and are likely to derive benefit from taking Semaglutide on top of their usual level of care.
"Our findings show that the magnitude of this treatment effect with semaglutide is independent of the amount of weight lost, suggesting that the drug has other actions which lower cardiovascular risk beyond reducing unhealthy body fat.
"These alternative mechanisms may include positive impacts on blood sugar, blood pressure, or inflammation, as well as direct effects on the heart muscle and blood vessels, or a combination of one or more of these."
However, the researchers warn there isn't yet evidence that treatment prevents major cardiovascular events.
Semaglutide, the active ingredient of Wegovy, is part of a growing class of GLP-1 drugs that make people feel full, reducing their calorie intake.
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