The study, published in the British Medical Journal, found that patients using these ‘slimming jabs’ can shed around a fifth of their body weight. But once the treatment stops, weight returns at an average pace of 0.8 kg per month, meaning most people could be back to their starting point within a year and a half.

‘People need to understand that the pounds can come back quickly when the treatment ends,’ warns Dr. Susan Jebb from Oxford University. She adds that the current figures come from clinical trials, so real life patterns may differ, and longer-term research is still needed.

By contrast, conventional dieting tends to produce slower but steadier results, with weight creeping back at roughly 0.1 kg per month. While the initial losses are smaller, the rebound is less dramatic.

Experts say the way GLP 1 drugs work in the brain may explain the rapid regain. These injections mimic a natural hormone that controls appetite. Dr. Adam Collins from the University of Surrey explains. ‘When you stop, the body’s own appetite control is weakened, and overeating becomes much easier.’

Many users describe it as flipping a switch. One woman said, ‘It felt like my body suddenly told me, ‘Go on, eat everything, you’ve been so good!’

The NHS currently recommends these injections only for people with obesity-related health risks, not for cosmetic slimming. Doctors stress that lifestyle changes healthy eating and exercise remain essential to keeping weight off.

Around 1.6 million UK adults have used these injections privately in the past year, and another 3.3 million are interested in trying them, according to surveys by Cancer Research UK. Women are twice as likely as men to use them, especially in their 40s and 50s.

Prof Naveed Sattar of Glasgow University notes the potential benefits. ‘Even a short term drop in weight can ease pressure on joints, the heart, and kidneys. Ongoing use over several years may help people stay lighter than they could with diet alone.’

Pharmaceutical companies echo the same advice, weight loss injections work best alongside healthy habits, and stopping them often results in regaining weight. Novo Nordisk, maker of Wegovy, says, ‘Obesity is a chronic condition, and long-term management is needed, just like diabetes or high blood pressure.’

The message is clear, these jabs can jump-start weight loss, but without careful planning, the pounds may return faster than anyone expects.