A study estimates 1.6m adults in England, Wales and Scotland used weight-loss drugs such as Wegovy and Mounjaro between early 2024 and early 2025.
The research, published in BMC Medicine and funded by Cancer Research UK, found a further 3.3m people said they would be interested in using them over the next year.
A UCL team analysed survey responses from 5,260 people, designed to reflect the wider population, collected in early 2025.
Use of the drugs was twice as common among women as men, and higher among people aged 45 to 55 and those reporting psychological distress in the past month.
Levels of use were similar across social grades, but interest in taking the drugs was higher among more disadvantaged groups, where obesity is more common, suggesting demand not 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.
“We hope to gather more detailed data in future, monitoring how trends change over time.
Good data are important as large numbers of people are taking these drugs outside medical supervision and there is wide potential for misuse. NHS prescribing data only captures a small part of the picture.”
The medicines, known as GLP-1 agonists, work by mimicking a hormone that helps people feel fuller.
Most respondents using medication solely for weight loss reported taking Mounjaro, which typically costs about £200 a month.
Among those using medication for weight loss, 15 per cent said they were taking a drug not licensed for this purpose, which can carry safety risks if accessed without appropriate clinical supervision.
Co-author Professor Clare Llewellyn said: “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.”
Jo Harby, director of health information at Cancer Research UK, said: “As obesity rates rise in the UK, this study shows growing public interest in weight loss medication. While these drugs can aid weight loss, they’re not a silver-bullet, as evidence suggests most people regain weight after treatment.
“More research is needed on their long-term impact, how these drugs affect cancer risk, and how best to support people to maintain a healthy weight.
“These drugs should only be prescribed by healthcare professionals alongside continued care and advice on diet and activity.
“It’s also vital that everyone who needs it can access a range of weight-management support.
“The world around us shapes our health, and the UK Government must do more to create healthier environments for all.”
