Research from Oxford University, published in the British Medical Journal, suggests overweight people shed large amounts when using jabs - about a fifth of their body weight. However, once they stop using them, they regain 0.8 kg every month, on average. This means they return to their pre-treatment weight in a year-and-a-half.

Dr Susan Jebb, from the University of Oxford, said: ‘People buying these need to be aware of the risk of fast weight regain when the treatment ends.'

People who diet instead can expect to lose less weight than with the jabs, but put the weight back on more slowly - perhaps around 0.1 kg a month - the researchers found, although it does vary.

Meanwhile, a separate study by UCL researchers reveals an estimated 1.6 million adults in England, Wales and Scotland used drugs to help lose weight between early 2024 and early 2025.

The research, published in BMC Medicine and funded by Cancer Research UK, found that an additional 3.3 million people said they would be interested in using weight loss drugs over the next year.

They found that use of the drugs was twice as common among women compared to men and more common among people in middle age (aged 45-55), and those who reported psychological distress in the past month.

The team also found that levels of use were similar across social grades, but that interest in using drugs to support weight loss in future was greater among more typically disadvantaged groups, suggesting a demand not currently met by private prescriptions.

Lead author Professor Sarah Jackson, from the UCL Institute of Epidemiology & Health Care, said: ‘Our findings show that an estimated 4.9 million adults in Great Britain – nearly one in 10 – have recently used a drug to support weight loss or were interested in using one in the near future.

‘This usage far exceeds NHS England's initial goal of prescribing these drugs to 220,000 people over three years.

'We do not know about our survey respondents' BMI or health conditions, so it is not clear how far this reflects a genuine medical need or how often the drugs are used unnecessarily by people of a healthy weight.'

Co-author Professor Clare Llewellyn, from UCL Institute of Epidemiology & Health Care, added: ‘Weight-loss drugs like GLP-1 agonists could play an important role in improving the health of the nation. Our findings suggest many people are accessing these medications outside the NHS. This raises concerns about equity given the costs of these drugs, as well as the adequacy of supervision of treatment.'