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NIHR-funded research, led by the University of Oxford, has found that people who come off weight-loss injections such as semaglutide (Wegovy) and tirzepatide (Mounjaro) can regain the weight they’ve lost 4 times faster than those who use traditional dieting and exercising.
The Oxford-led research, published in the British Medical Journal, examined 37 studies, with over 9,000 participants, who stopped taking weight management medicines after being on them for an average of 39 weeks of treatment. Participants were followed for an average of 32 weeks after stopping.
The study found that weight can return quickly once these jabs are stopped. On average, people put on around 0.8 kg (1.8 pounds) per month after weight-loss drugs were stopped. This meant that people would return to their starting weight, on average, within 18 months.
Crucially, weight regain after stopping drugs was faster than traditional dieting and exercise support by approximately 0.3 kg (0.7 pounds) per month - independent of how much weight was initially lost.
The study was funded by NIHR Oxford Biomedical Research Centre (BRC) and NIHR Oxford Health BRC, and supported by NIHR Applied Research Collaboration Oxford and Thames Valley.
Lead author Dr Sam West, postdoctoral researcher at the Nuffield Department of Primary Care Health Sciences, University of Oxford, said: "These medicines are transforming obesity treatment and can achieve important weight loss. However, our analysis shows that people tend to regain weight rapidly after stopping – faster than we see with behavioural programmes.
"This isn't a failing of the medicines – it reflects the nature of obesity as a chronic, relapsing condition. It sounds a cautionary note for short-term use without a more comprehensive approach to weight management."
An estimated 9 in 10 people currently using weight-loss medicines in the UK are buying them privately, often without the comprehensive clinical oversight and behavioural support that accompanies NHS prescribing.
Professor Susan Jebb, joint senior author, said: "When people lose weight through changes to their diet and activity, they're practising the skills that help maintain that loss. It may be that with medication, the weight comes off without necessarily developing those skills. These findings underscore the need for a more holistic and long-term approach to weight management, and increased emphasis on the importance of primary prevention of weight gain.”
This follows on from another NIHR-funded study, published in Obesity Reviews, that looked at the gap between nutritional guidance for people using weight-loss drugs.
These drugs can reduce calorie intake by 16-39%, making them a powerful tool to help people living with obesity and overweight. However, there has been little research to examine their impact on diet quality, protein intake, or adequacy of vitamins and minerals. Evidence suggests that lean body mass – including muscle – can constitute up to 40% of total weight lost during treatment.
Dr Adrian Brown, an NIHR Advanced Fellow from the Centre of Obesity Research at UCL and the study’s corresponding author, said: “Obesity management medications work by suppressing appetite, increasing feelings of fullness, and altering eating behaviours, which often leads people to eat significantly less. This can be highly beneficial for individuals living with obesity, as it supports substantial weight loss and improves health outcomes.
“However, without appropriate nutritional guidance and support from healthcare professionals, there is a real risk that reduced food intake could compromise dietary quality, meaning people may not get enough protein, fibre, vitamins, and minerals essential for maintaining overall health.”
The study received additional support from the Medical Research Council and the NIHR UCLH Biomedical Research Centre.
Current evidence is limited, with only 12 studies looking at nutrition during weight-loss treatment. Because these studies were all conducted differently, researchers say more consistent data is needed to create the best possible guidance for patients.
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