Experts have called for robust support for people using weight loss jabs to prevent them from piling on the pounds when they stop taking the drugs.
Researchers at the University of Oxford discovered that people on drugs such as semaglutide – marketed under names such as Wegovy, Ozempic and Rybelsus – and tirzepatide, marketed under the name Mounjaro, lose weight during treatment, but regain it within 20 months of stopping the jabs – four times faster than traditional dieters.
In comparison, the study found those who are supported to lose weight through healthier diets and exercise keep the weight off for about four years.
Around 1.5 million people are currently using weight loss jabs in the UK. While there is no limit on how long someone can take Mounjaro, Wegovy can only be prescribed on the NHS for two years.
Studies suggest half of people stop taking the drugs, either due to the cost of paying for the jabs privately, side effects or because they have reached their weight loss goal.
“The vast majority of people, particularly those with high BMIs are supposed to be on the jabs long term because it’s a chronic condition,” Naveed Sattar professor of metabolic medicine at the University of Glasgow told The Independent.
“When you stop a jab the food noise comes back straight away, whereas when you’re losing weight through lifestyle changes, you’re a different type of person because you’re motivated, you’re learning skills.
“For some people, a small number of lifestyle changes alone will work. Others will need the jab and their ability to make lifestyle changes improves.”
The study published in the British Medical Journal (BMJ), included 37 studies involving more than 9,000 people.
They had an average treatment time of 10 months, and average follow-up of eight months.
People on any type of weight loss medication lost an average of 8.3kg during treatment, but regained 4.8kg within the first year and were back to their original weight within 1.7 years of stopping the drugs.
Those specifically on Wegovy and Mounjaro lost just under 15kg but regained 10kg within the first year of stopping treatment.
They regained all their weight within 1.5 years, according to projections in the study based on one year of data.
All cardiometabolic markers – such as blood glucose and cholesterol – also return to baseline 1.4 years after stopping medication.
Sam West, author on the study and postdoctoral researcher at the University of Oxford, said people taking the drugs regain weight four times faster than those using diet and exercise alone.
Weight-loss injections, also known as GLP-1 receptor agonists, work by mimicking the natural hormone which regulates blood sugar, appetite and digestion.
Dr Adam Collins, associate professor of nutrition at the University of Surrey, explained the rapid weight gain could be due to the body becoming used to the GLP-1 drug and therefore less sensitive to its effects.
“No problem when taking the drugs, but as soon as you withdraw this GLP-1 ‘fix’, appetite is no longer kept in check, and overeating is far more likely,” he said.
Susan Jebb, professor of diet and population health at the University of Oxford and adviser to ministers and the NHS on obesity, suggested people may need a lifetime solution – such as obesity jabs or behaviour change support or both – to tackle obesity in the long-term.
She said: “Obesity is a chronic relapsing condition, and I think one would expect that these treatments need to be continued for life, just in the same way as blood pressure medication.”
She said that when people are offered behavioural programmes focused on diet and exercise alongside drug treatment, this increases the amount of weight people lose.
“However, when the drug stops and appetite returns, it seems that those strategies are not sufficient to enable people to continue to manage their weight,” she said.
“In contrast, in behavioural programmes where people haven’t had the extra assistance of drugs, they probably have to practice those strategies more, and maybe they therefore are more persistent over time.”