Individuals using obesity medications such as Mounjaro or Wegovy are likely to regain almost two-thirds of the weight they lose within a year of stopping the drugs, a new study suggests.
While this period of post-treatment weight gain is expected to plateau, patients typically manage to keep a quarter of the weight lost off.
Despite this, researchers have cautioned that if the regained weight is predominantly fat, people could “be worse off than before” they started the jabs.
These weight loss injections are a class of drugs known as GLP-1 receptor agonists, which work by mimicking the GLP-1 hormone to regulate blood sugar and insulin levels.
Initially developed as a treatment for type 2 diabetes, certain types like semaglutide (Wegovy) and tirzepatide (Mounjaro) are approved for use on the NHS to help tackle obesity.
The study by researchers at the University of Cambridge included six trials involving more than 3,200 people.
The analysis suggests that after stopping the jabs for 52 weeks, on average people regained 60% of the weight they lost.
Researchers said the findings, published in eClinicalMedicine, “indicate that there is significant weight regain following cessation of GLP-1RAs”.
However, by 60 weeks, researchers said the regain started to taper off at 75 per cent of the original weight lost, suggesting 25 per cent may be sustained in the long-term.
Brajan Budini, a medical student at the School of Clinical Medicine and Trinity College, University of Cambridge, said: “Drugs such as Ozempic and Wegovy act like brakes on our appetite, making us feel full sooner, which means we eat less and therefore lose weight.
“When people stop taking them, they are essentially taking their foot off the brake, and this can lead to rapid weight regain.
“Our projections show that even though people regain most of the weight they have lost, they still maintain some of the weight loss, but what we currently don’t know is if the same proportion of lean mass is recovered.
“If the regained weight is disproportionately fat, individuals may ultimately be worse off than before in their fat-to-lean mass ratio, which may have adverse consequences for their health.”
Researchers called for future trials to explore the the effect of GLP-1RAs on the composition of weight loss during and after treatment.
They added that current prescribing guidelines for GLP-1RAs “are inconsistent and largely inadequate in addressing the risk of weight regain following treatment cessation”.
For example, the National Institute for Health and Care Excellence recommends that patients should be on semaglutide for weight loss for a maximum of two years, although there is no such limit for tirzepatide.
Steven Luo, also a medical student at the School of Clinical Medicine and Trinity College, added: “When stopping weight loss drugs, doctors and patients should be aware of the potential for weight regain and consider ways to mitigate this risk.
“It’s important that people are given advice on improving their diet and exercise, rather than relying solely on the drugs, as this may help them maintain good habits when they stop taking them.”
