Weight-loss injections, seen as a breakthrough for obesity treatment, may require lifelong use or need to be combined with major lifestyle changes to avoid regaining the lost weight, a new study by Oxford University researchers has revealed.

The study, which examined data from 11 trials involving over 6,300 patients, found that while these drugs can lead to an average weight loss of 8 kg, patients typically return to their original weight within 10 months of discontinuing treatment.

Popular weight-loss medications, such as those containing semaglutide (example- Wegovy) or tirzepatide (example – Mounjaro), work by mimicking hormones that regulate appetite, helping users feel fuller and consume fewer calories. These drugs have transformed obesity management, offering hope to millions struggling with weight-related health issues. However, the Oxford findings underline that without sustained behavioral changes, the benefits of these injections may be short-lived.

“These drugs are very effective at helping you lose weight, but when you stop them, weight regain is much faster than [after stopping] diets,” Co-author of the study, Professor Susan Jebb, an expert in diet and population health at the University of Oxford, said.

“Is it going to be worth the NHS investing in these drugs if they only have them for a short time and then they pile all the weight back on, or does the NHS have to accept that these are going to be long-term therapies?” he added.

Presented at the European Congress on Obesity in Malaga, Spain, the study didn’t pinpoint the exact reasons for weight regain, but Professor Susan Jebb suggested that GLP-1 receptor agonists (a class of medications used to treat type 2 diabetes and obesity), which suppress appetite, allow users to lose weight without actively practicing dietary restraint or adopting sustainable lifestyle habits. This dependence on the drugs’ hunger-curbing effects may lead to rapid weight regain once treatment is paused. 

The cost and accessibility of weight-loss injections also raise concerns about their lifelong use. In the UK, one month supply of Wegovy can cost hundreds of pounds. And while some health systems, like the National Health Service (NHS), offer subsidized access for eligible patients, long-term funding remains uncertain.

Side effects such as nausea, fatigue, and, in rare cases, more serious complications may also deter some patients from prolonged use.

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