According to data published in the British Medical Journal, overweight patients using injections lose about 20% of their total body weight. However, after stopping the injections, they begin to gain approximately 0.8 kg per month.
This results in them returning to their original weight within 18 months.
Researcher Susan Jebb from the University of Oxford emphasizes: “By purchasing these medications, people should be aware of the risk of rapid weight regain after treatment ends.”
She also notes that the findings are based on medical research data rather than real-world observations, and further studies are needed to explore the long-term effects of using new weight loss injections.
In analyzing 37 studies involving more than 9,000 patients, scientists compared the results of popular injections with traditional diets and other weight loss methods.
However, only eight of these studies focused on GLP-1 medications, such as Wegovy and Mounjaro, with a maximum follow-up period of one year after stopping the treatment, making the conclusions drawn approximate.
Researchers noted that while patients lose fewer kilograms through dieting than with injections, after completing a diet, weight returns more slowly—about 0.1 kg per month, depending on individual factors.
Risk of Relapse
The National Health Service (NHS) of the UK recommends injections for overweight individuals who have accompanying health risks but does not advise them for those who simply want to lose a little weight.
Additionally, doctors should recommend lifestyle changes to patients, including a balanced diet and physical activity, to help them maintain their achieved weight.
Many experts believe that treatment should be viewed as long-term, considering the likelihood of relapse.
Patients who stop injections report experiencing a “sudden feeling of intense hunger.”
One woman shared: “I felt like something clicked in my head and said, ‘Eat everything, you deserve it, you haven’t eaten for so long.’”
Dr. Adam Collins, a nutrition specialist from the University of Surrey, claims that the mechanism of action of these medications on the brain and body may explain the rapid weight regain after their use ends.
The fact is that they mimic the GLP-1 hormone, which is responsible for appetite control.
“Prolonged artificial maintenance of GLP-1 levels significantly above normal can lead to decreased production of one’s own hormone and reduced sensitivity to its effects,” he explains. “During the use of the medications, there are no issues, but after stopping their use, appetite becomes uncontrollable, increasing the risk of overeating.”
According to Collins, going through this process is a real challenge.
“The situation is exacerbated when a person relies solely on the action of GLP-1 to suppress appetite and does not make changes to their diet or habits that could help in the long term,” adds the doctor.
Recent data shows that last year about 1.6 million adults in the UK used weight loss injections, primarily obtaining them through private prescriptions rather than through the NHS program.
According to Cancer Research UK, based on a nationwide survey 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 try.
Moreover, women sought these injections twice as often as men, especially among those aged 40 to 50.
Chronic Nature of Obesity
Professor Naveed Sattar from the University of Glasgow notes that weight loss injections may provide additional health benefits as they promote rapid weight loss.
“Losing weight for just two to three years through short-term use of these medications can help slow down damage to joints, the heart, or kidneys. Larger and longer-term studies are needed for a more detailed examination of this issue,” he says.
“It is important to understand that long-term use of these medications over three to four years helps people maintain weight at significantly lower levels, which is usually not achieved through lifestyle changes, as many people regain lost kilograms over time,” adds Sattar.
Doctors and weight control specialists cannot simply prescribe Mounjaro and Wegovy, even if a patient previously received them through a private prescription. Medications are prescribed only to those who genuinely need them for medical reasons and meet certain criteria, such as having health problems due to being overweight.
Currently, there are no prescription duration limits for Mounjaro in the NHS, whereas Wegovy can be prescribed for no more than two years.
A representative from Eli Lilly, the manufacturer of Mounjaro, noted that the use of weight loss medications should be accompanied by proper nutrition, physical activity, and medical supervision.
“After treatment ends, weight may return, which is related to the biological nature of the disease, not a lack of effort,” she added.
“These findings highlight the chronic nature of obesity and indicate the need for ongoing treatment to maintain improvements in weight and overall health for patients, as is done with other chronic conditions such as diabetes or hypertension,” stated the pharmaceutical company Novo Nordisk, the manufacturer of Wegovy.
