People who stop using popular weight-loss injections such as Wegovy or Mounjaro may regain their lost weight far more rapidly than those who rely on conventional dieting and exercise, according to new research published in the British Medical Journal (BMJ).
The analysis suggests that while injectable weight-loss drugs can lead to dramatic reductions in body weight—often around 20%—the benefits may fade quickly once treatment ends.
On average, people who stop the injections regain around 0.8 kilograms per month, meaning they could return to their original weight within 18 months.
By contrast, individuals who lose weight through traditional methods such as diet and exercise tend to regain weight more slowly, at roughly 0.1 kilograms per month, although outcomes vary widely.
Dr Susan Jebb of the University of Oxford, one of the study’s investigators, said people considering the injections need to understand the risks.
“People buying these need to be aware of the risk of fast weight regain when the treatment ends,” she warned, adding that longer-term real-world studies are still needed.
The researchers reviewed 37 clinical trials involving more than 9,000 participants. Only eight of these studies focused on newer GLP-1 drugs, including Wegovy and Mounjaro, with follow-up limited to about one year after stopping treatment.
As a result, the weight regain figures represent estimates rather than long-term certainties.
GLP-1 drugs work by mimicking a natural hormone that regulates appetite and feelings of fullness. According to Dr Adam Collins, a nutrition expert at the University of Surrey, prolonged use may suppress the body’s own hunger-regulating systems.
When treatment stops, appetite can rebound sharply, making overeating more likely.
Some users describe coming off the injections as an abrupt and difficult experience, with hunger returning suddenly. Experts say this effect is worsened if patients rely solely on medication without adopting sustainable eating or behavioural changes.
The NHS currently recommends weight-loss injections only for people who are obese and have related health conditions, not for cosmetic weight loss. Doctors are also advised to prescribe lifestyle changes alongside medication to improve long-term outcomes.
Despite concerns, some specialists argue that the drugs still offer significant health benefits. Professor Naveed Sattar of the University of Glasgow said maintaining lower weight for even a few years could reduce strain on joints and vital organs.
He noted that continued use over several years helps many people maintain weight loss more effectively than lifestyle changes alone.
Around 1.6 million UK adults are estimated to have used weight-loss injections in the past year, mostly through private prescriptions. With interest growing rapidly, researchers say the findings underline a key message: obesity is a chronic condition, and long-term management—rather than short-term fixes—may be essential.
