London: People who stop using popular weight-loss injections such as Mounjaro and Wegovy may regain the weight they lost far more quickly than those who rely on traditional dieting and exercise, according to new research published in the British Medical Journal.
The analysis suggests that while the injections help users shed a significant amount of weight, roughly 20 percent of their body mass, the kilos can return rapidly once treatment ends. On average, former users regain about 0.8kg per month, meaning many are back to their original weight within 18 months.
By contrast, people who lose weight through diet and physical activity typically regain weight much more slowly, at around 0.1kg per month, although results vary widely.
Warning over rapid regain
Dr. Susan Jebb of the University of Oxford, one of the study’s investigators, said people considering the injections should be fully aware of what can happen after stopping treatment. Dr. Jebb added that longer-term studies are needed to understand the lasting effects of the new drugs.
How the study was conducted
Researchers reviewed 37 studies involving more than 9,000 participants, comparing weight-loss injections with conventional approaches such as dieting, exercise and older weight-loss medications. Only eight studies focused on newer GLP-1 drugs like Wegovy and Mounjaro, with follow-up lasting no more than a year after treatment stopped, meaning the figures remain estimates.
Why hunger comes back stronger
Experts say the way these drugs work may explain the sharp rebound. The injections mimic GLP-1, a hormone that suppresses appetite.
Dr. Adam Collins, a nutrition specialist at the University of Surrey, explained that prolonged exposure to artificially high GLP-1 levels may reduce the body’s own hormone production or sensitivity.
This effect can be worse if users rely solely on the injections without building long-term dietary or behavioural habits. Some former users describe stopping the medication as an abrupt and overwhelming experience, with hunger returning like a switch being flipped.
Growing popularity, limited access
An estimated 1.6 million UK adults have used weight-loss injections in the past year, most through private prescriptions. A further 3.3 million people say they would consider using them, according to Cancer Research UK — meaning around one in 10 adults has tried or is interested in the drugs.
Use is reportedly higher among women and most common among people in their 40s and 50s. The NHS currently recommends the injections only for people who are obese and have related health conditions.
Access remains limited, and even patients who received private prescriptions cannot automatically continue treatment through the NHS. Wegovy is capped at two years of use, while Mounjaro currently has no fixed NHS time limit.
Obesity as a long-term condition
Professor Naveed Sattar of the University of Glasgow said the drugs can still offer meaningful health benefits, particularly if they reduce weight quickly.
Both manufacturers behind the drugs emphasised that weight-loss injections should be used alongside lifestyle changes. Eli Lilly, which produces Mounjaro, said weight regain reflects the biology of obesity rather than a lack of effort. Novo Nordisk, the maker of Wegovy, said the findings underline obesity’s chronic nature and suggest ongoing treatment may be necessary, similar to conditions such as diabetes or high blood pressure.
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