Oxford study finds people rapidly gain fat after stopping weight-loss injections

New research suggests that people who use popular weight-loss injections, such as Wegovy and Mounjaro, may regain lost weight significantly faster once treatment stops, compared to those who lose weight through diet and exercise alone.

The findings come from a study led by researchers at the University of Oxford, contributing to the growing debate about the long-term role of so-called GLP-1 weight-loss drugs.

Faster weight regain

According to the study, people who discontinued weight-loss medication were estimated to return to their original weight within about 1.7 years. By contrast, those who stopped traditional behavioural weight-loss programmes were projected to regain the weight only after four years.

Lead author Dr Sam West, a postdoctoral researcher at Oxford, said weight regain is common after any form of weight loss, but the speed observed after stopping medication stood out.

Why the weight comes back quicker

Researchers believe the difference may lie in habit formation. Behavioural programmes typically focus on long-term skills such as managing hunger, eating cues and portion control.

In contrast, GLP-1 medications work by suppressing appetite. Once the injections stop, hunger signals return, often without the coping mechanisms needed to manage them.

“We think people may not have developed the skills needed to maintain weight loss once treatment ends,” West explained.

Long-term effects still unclear

While similar drugs have been used for diabetes for more than a decade, weight-loss treatments usually involve higher doses. Researchers say there is still limited long-term data on what happens to people who take these medications for several years at those levels.

Existing diabetes data offers reassurance, but scientists stress the need for studies tracking weight, health, and metabolism five to 10 years after treatment ends

Not a silver bullet for obesity

Despite the findings, researchers say weight-loss injections remain an effective tool, but not a cure-all.

Obesity, they argue, is a chronic and relapsing condition that may require long-term treatment, whether through sustained medication use, behavioural support, or a combination of both.

West said people considering these drugs should do so with realistic expectations. “They work while you take them,” he said, adding that anyone starting treatment should plan for long-term use or commit to meaningful behaviour change alongside medication.

The bottom line

Weight-loss injections can help people shed significant weight, but the research suggests stopping suddenly, especially withoutlifestyle changes, may lead to rapid regain.

Experts say future research must focus on how best to maintain weight loss over the long term, rather than relying on short courses of medication alone.

For more information, listen to West using the audio player below: