The weight loss jabs Mounjaro and Wegovy may need to be continued for life to keep obesity under control, new research suggests.
The finding will dismay people who are stretching their household finances to afford treatment, which can cost up to £300 a month depending on the dose and drug.
Almost two million British adults have used the jabs in the last year. And the overwhelming majority are paying privately.
According to the new research, around half of users stop treatment within a year. That’s often because of side effects or cost.
But it then takes an average of just one and a half years for people to put back on all the weight they’ve lost, results published in the British Medical Journal reveal.
Professor Susan Jebb, an expert on diet and population health at the University of Oxford, told Sky News it suggests treatment may need to be long-term.
“Most people who are living with obesity, who have all that genetic and metabolic predisposition to gain weight, are going to need lifelong support of some kind,” she said.
“Whether that’s lifelong medication or whether it’s medication at intervals combined with some other treatments, we just don’t yet know.
“The big unanswered question is how do you help people keep the weight off. And that is a different process than is necessary for losing weight.”
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Rosie Parsons lost eight stone while taking Wegovy, dropping from 19.5 stone to a little over 11 stone.
Rosie before weight loss drugs – at 19 stone
Rosie Parsons at 11 stone after her stunning weight loss transformation
But when her weight loss began to slow, she questioned the value of spending around £175 a month on the drug.
She tried using Mounjaro, which is even more powerful, but the gastrointestinal side effects were too much.
In the four months since stopping treatment she put on four stone – half of what she lost.
Rosie at her current “rebound” weight of 15 stone
“I’m just trying to figure out what to do,” she said.
“It’s difficult when the price of everything has gone up so much as well.
“It probably does mean that I’ll need to be on those drugs for life. But it’s how to afford that because I can’t get treatment through the NHS.”
Rosie still finds it reasonably straightforward to have a healthy diet during the day. But without the jabs, the sugar cravings return in the evening.
Between 40% and 70% of the risk of obesity is determined by genetics. Inheriting the wrong genes doesn’t make obesity inevitable, but it makes it harder to control weight – particularly when unhealthy food is cheap and abundant.
How the weight loss drugs work isn’t fully understood. They mimic gastric hormones and make people feel fuller for longer. But they also have an effect on the brain.
The research shows that people put on weight four times faster after quitting the jabs than coming off a diet.
Scientists say that may be because the biological switches that drive obesity are suddenly flicked back on when treatment with such powerful drugs is stopped.
Sam West, another of the Oxford researchers, said: “They’re not a silver bullet, they don’t fix it long-term. While you take them, they are incredibly effective. But when you stop taking them, the weight regain occurs rapidly.”
