Studies show that overweight patients lose about 20% of their body mass while receiving injections; however, after stopping treatment, they gain an average of 0.8 kg per month.
Thus, after a year and a half, they return to their original weight.
Susan Jebb, a researcher from the University of Oxford, emphasizes that users of these medications should be aware of the risk of rapid weight gain after therapy ends.
However, she notes that the data is based on clinical trials and does not account for real-world practice, highlighting the need for further research regarding the long-term effects of new weight loss medications.
During the analysis of 37 studies involving over nine thousand participants, researchers compared the results of injections with traditional weight loss methods, such as diets and other medications.
Only eight of these studies examined the new GLP-1 drugs, such as Wegovy and Mounjaro, with a maximum follow-up period of one year after stopping the medication, making the results obtained approximate.
Although injections lead to greater weight loss than diets, after completing a dietary regimen, weight returns more slowly—about 0.1 kg per month, although this depends on individual factors.
Risk of Relapse
The National Health Service (NHS) in the UK prescribes injections to those with serious health risks due to obesity but does not recommend them for those who simply want to lose a little weight.
Doctors should also offer their patients lifestyle changes, including healthy eating and regular physical activity, to help with weight control.
Many specialists believe that such treatments should be viewed as long-term, given the high risk of weight regain.
People who stop injections report that it feels like a "switch" has been flipped, triggering intense hunger.
One participant shared, "It felt like something clicked in my head and said, 'Eat everything, you deserve it, you haven't eaten anything for so long.'"
Dr. Adam Collins, a nutrition specialist from the University of Surrey, explains that the mechanism of action of these drugs may be the reason for the rapid weight regain after their discontinuation.
The medications mimic the GLP-1 hormone, which regulates appetite.
"Prolonged artificial maintenance of high levels of GLP-1 may lead to reduced production of the natural hormone and decreased sensitivity to its actions," he says. "While a person is taking the medications, there are no problems, but after stopping them, appetite becomes uncontrollable, increasing the risk of overeating."
According to Collins, going through this process can be quite challenging.
"The situation is exacerbated if a person relies solely on the action of GLP-1 and does not strive to change their habits or diet, which could help in the long term," adds the doctor.
According to the latest data, about 1.6 million adults in the UK used injections for weight loss last year, primarily through private prescriptions rather than the NHS.
According to a study by Cancer Research UK conducted in the first quarter of 2025, another 3.3 million people expressed a desire to try "slimming injections," meaning that one in ten adults has either already used them or would like to.
At the same time, women used injections twice as often as men, and they were most commonly used among people aged 40 to 50.
Chronic Nature of Obesity
Professor Naveed Sattar from the University of Glasgow notes that weight loss injections can benefit health as they promote rapid weight loss.
"Losing weight for two to three years through short-term use of these medications can slow down damage to joints, heart, or kidneys. More research is needed for a deeper understanding of this issue," he says.
"It is important to emphasize that long-term use of these medications over three to four years can help people maintain significantly lower weights, which is not always observed with weight loss through lifestyle changes, as most people regain lost weight over time," Sattar adds.
Doctors and weight management specialists cannot simply prescribe Mounjaro and Wegovy, even if a patient has already used them through a private prescription. The medications are prescribed only to those who need them for medical reasons and meet certain criteria, such as having health issues due to excess weight.
Currently, there are no restrictions on the duration of prescriptions for Mounjaro in the NHS, while Wegovy can be prescribed for no more than two years.
A representative of the pharmaceutical company Eli Lilly, which produces Mounjaro, noted that the use of weight loss medications should be accompanied by proper nutrition, physical activity, and medical supervision.
"Weight regain after treatment cessation is related to the biological nature of the disease, not a lack of effort," she added.
"These results highlight the chronic nature of obesity and the need for ongoing treatment to maintain improvements in weight and overall health, as is the case with other chronic diseases such as diabetes or hypertension," stated the company Novo Nordisk, which produces Wegovy.
