One in five adults have used a weight-loss treatment, such as diet pills or injections – without consulting a doctor, according to research. A study of 2,003 adults found 29 percent of these bought the treatment on illegitimate sites, while a quarter used someone else’s prescription – and 24 percent were able to make the purchase through social media.

It also emerged 19 percent are more likely to try a product endorsed by celebrities – causing doctors to warn against the ongoing “celebrification” of weight-loss treatments.

Dr Crystal Wyllie, from Asda Online Doctor, which commissioned the research to mark the launch of its weight-loss injection guide, said: “Weight-loss treatments, like Wegovy, provide an important service for patients affected by excessive weight, or struggling with a weight-related health condition.

“It’s concerning to see so many healthy adults looking to lay their hands on these treatments, which should be reserved for those with a genuine medical need.

“It is now down to us as providers to ensure that proper safeguarding is put in place for all patients – and we hope to see other stockists following our suit, and implementing rigorous checks to make sure that these treatments are administered responsibly.”

Weight-loss injections have been created specifically for individuals with a BMI over 30, or at a lower BMI with certain risk factors, such as high blood pressure or diabetes.

However, the study found that, of the 35 percent of adults who would be interested in accessing weight-loss injections in the UK, only seven percent without pre-existing conditions would meet the criteria.

Men are also more likely to purchase these unprescribed treatments than women (25 percent, versus 20 percent).

And it is most common among young people, with 46 percent of those aged 18-24 likely to make a purchase – twice as many as the national average of 22 percent.

A spokesman for Asda Online Doctor added: “This trend can be highly dangerous, because weight-loss injection brands such as Wegovy, and the latest-to-market, Mounjaro, require prescriptions.

“Injection pens purchased through illegitimate sources may contain harmful ingredients not on the label, leading to potentially dangerous side-effects.”