People who stop using weight loss injections, such as Manjaro (Mounjaro) or Vegs (wegovy), can regain lost weight four times faster than those who give up on classic diets and exercise, new research suggests.
Those who are slightly overweight lose a lot of weight during treatment with these injections - on average about a fifth of their total body weight - but after stopping treatment, they regain an average of about 0,8 kilograms per month, the data show. British Medical Journal.
This means that they return to the body weight they had before starting therapy in about a year and a half.
"People who buy these drugs need to be aware of the risk of rapid weight regain after stopping treatment," warns Dr. Susan Jebb, one of the study's authors from the University of Oxford in the United Kingdom.
She emphasizes that the findings are based on clinical trials, not real life, and that additional studies are needed on the long-term effects of the new weight-loss injections.
Researchers analyzed 37 studies - involving more than 9.000 patients - and compared the effects of the most famous weight loss injections with the effects of classic diets and diet pills.
Only eight studies looked at therapy with newer GLP-1 (glucagon-like peptide-1) drugs, such as Vegovi and Manjaro, and the longest follow-up period for patients after stopping therapy was one year, so the data presented here represent the researchers' estimates.
People who diet usually lose less weight than those who use injections, but after stopping the diet, weight returns much more slowly - perhaps about 0,1 kilogram per month, although there are large individual differences, the researchers say.
Short-term solution?
The British National Health Service (NHS) recommends these injections for people who are overweight and have health risks associated with obesity, not for those who just want to lose weight.
In addition to therapy, doctors should also prescribe lifestyle changes - a healthy diet and sufficient physical activity to maintain body weight in the long term.
Many experts believe that this type of therapy should be lifelong, given the high risk of weight regain.
People who have tried to quit using injections often describe the experience as "a switch being flipped and you're immediately very hungry."
"It was like something opened up in my head and said, 'Eat everything, come on, you deserve it because you haven't eaten anything in a long time,'" one woman said.
The way these injections affect the brain and body may explain why weight regain is so pronounced after stopping treatment, says Adam Collins, a nutrition expert at the University of Surrey in England.
These injections mimic the natural hormone GLP-1, which regulates hunger.
"Artificially providing GLP-1 levels that are several times higher than normal for a prolonged period of time can cause the body to produce less natural GLP-1, and the body can also become less sensitive to its effects."
"This is not a problem while the medication is being taken, but as soon as that 'dose' of GLP-1 is stopped, appetite is no longer under control and overeating becomes much more likely."
Abruptly stopping therapy is extremely difficult, he points out.
"The situation is even worse if someone relies entirely on GLP-1 to 'do all the work', artificially suppressing appetite, without making any dietary and behavioral changes that would help in the long term."
According to the latest estimates, around 1,6 million adults in the UK have used these types of injections in the past year.
They were mostly purchased on prescriptions issued in private practices, not through the NHS.
Another 3,3 million people say they would be interested in using weight loss injections next year.
That means one in ten adults has either tried the injections or would like to use them, according to the cancer research charity. Cancer Research UK, based on surveys from the first quarter of 2025.
Women were twice as likely to use these injections as men, especially people in their fourth and fifth decades of life.
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Obesity is a chronic condition
The injections may have additional health benefits because they reduce body weight quickly, according to Professor Navid Sattar from the University of Glasgow.
"Lower body weight over two to three years thanks to short-term use of these injections can probably slow down damage to joints, heart and kidneys," he says.
However, he says, for this to be widely applied, more extensive and longer-term studies will be needed.
"It is important to note that continuous use of these medications for three to four years allows people to maintain a significantly lower body weight than they would have been able to without the medication, a benefit not typically seen with weight loss achieved solely through lifestyle changes, when many people regain the weight over time."
General practitioners and weight management services cannot automatically prescribe Manjaro or Vegovi, even if the patient has previously been prescribed the drug in private practice.
Medications can be offered to people who need them most and who meet certain criteria, for example if they have a weight-related health problem.
Through the NHS, Vegova is prescribed for a maximum of two years, and there is currently no time limit set for Manjaro.
The pharmaceutical company Eli Lilly, which produces Manjaro, emphasizes that people taking weight loss drugs must also eat healthily, be physically active, and be under medical supervision.
"When therapy is stopped, weight may return, reflecting the biology of the condition, not a lack of effort."
Pharmaceutical company Novo Nordisk, which produces Vegovi, added that "the findings highlight that obesity is a chronic condition."
"They suggest that ongoing therapy is necessary to help patients maintain a healthier weight and overall health, similar to the treatment of other chronic diseases, such as diabetes or high blood pressure."
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