Weight-loss drugs, such as Ozempic, Mounjaro and Wegovy may lead to people losing weight but a review of trials conducted on thousands of adults shows that many regain weight soon after they stop using the medication.
Weight-loss drug users, on average, regain weight at a rate of 0.4 kilograms per month after they stop taking their weight-loss medications, a review of 63 trials covering more than 9,000 individuals published in the British Medical Journal on Wednesday found.
Of these, around 6,000 were on GLP-1 drugs such as semaglutide or tirzepatide and had stopped taking them, while around 3,000 were on behavioural weight management programmes (BWMPs) that include a mix of counselling, diet, exercise and other support measures.
The trials were conducted up to February 2025.
Patients who went on the weight-loss drugs and then stopped them regained their entire baseline weight on average around 20 months after they stopped taking the drugs.
Patients who stopped taking some of the newer drugs included in the research — semaglutide or tirzepatide — saw their weight return at a much faster rate (0.8 kg/month) and regained their baseline weight much faster, in around 18 months on average.
For many experts, the study only confirms what they already know.
“What the paper finds, very unsurprisingly, is that when you stop a drug that is prescribed to cause weight loss, then people begin to regain their weight,” said Dr. Hertzel Gerstein, professor of medicine and endocrinologist at McMaster University.
The effects of GLP-1 drugs such as semaglutide or tirzepatide are temporary and go away once a patient stops using them, said Jennifer Lake, assistant professor at the University of Toronto’s Leslie Dan Faculty of Pharmacy.
The challenge is that when a patient stops taking their medication, the drug is gone but their “food environment” remains the same, said Dana Small, professor at McGill University and a Canada Excellence Research Chair in metabolism and the brain.
The “food environment” refers to the physical, political, economic and sociocultural factors that contribute to the kind of food that a person has access to. For many Canadians and Americans, that usually means a plethora of ultra-processed foods.
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Patients who stopped behavioural weight management programs also regained weight, albeit at a much slower rate – 0.2 kg per month.
Relying on exercise and diet, as opposed to GLP-1 drugs, will mean “neither as much weight loss but also slower and not as much as weight regain,” Small said.
Patients who go off the weight-loss medications also run the risk of other benefits going away, the research shows. That includes benefits for a person’s heart and cardiovascular system, which are often improved as a result of the weight loss that comes from the medications.
“When you go off the GLP-1 medicines, as the study showed, you also lose the cardiometabolic benefits,” Small said.
All these markers returned to the baseline level after around 16-17 months of patients stopping these medications, the study shows.
This means a return of the risk of conditions like cardiovascular disease, high cholesterol and hypertension, Lake said.
“When you gain back the weight, you go back to having those high-risk things,” she added.
Older patients also run the risk of losing not just weight but also lean muscle mass.
“That can put people at risk of falls and frailty,” Lake said.
However, Gerstein warns against referring to this effect as a “rebound” or “yo-yo” effect.
This is because the drugs themselves don’t alter the patient’s physiology permanently.
“They have a pharmacologic effect. They have a drug effect, and the drug effect does many things to the body — many good things. But when you stop the drug, that drug effect is gone,” he said.
The BMJ review also has many limitations, he added.
“All of the data here are observational data and not experimental,” Gerstein said.
“There’s really nothing surprising about it, and there’s nothing to be alarmed about this. This just tells you that the drug works while you’re taking it.”
Evidence in the BMJ research “cautions against short term use of WMMs” (weight management medications).
“We’re saying to people: when they’re using them for weight loss, this is probably a chronic medication for you. You’re probably going to be on it forever,” Lake said.
For many patients struggling with obesity, these medications have been a “game-changer,” said Dr. Sonja Reichert, associate professor in the Department of Family Medicine at Western University.
“We understand how complex obesity is now. It involves our genes and hormones and so many things that we have zero control over. People have often tried every diet or have tried every exercise plan and still haven’t been able to achieve their weight management goals,” she said.
When used in combination with exercise and diet, GLP-1 drugs can be helpful to some patients, Small said.
“If you have access, it’s still a good thing to take the medications to lose the weight. You have benefits until you regain the weight, but you can supplement with things like behavioural weigh- loss programs,” she said.
GLP-1 drugs are “definitely not a panacea” for weight loss, she said.
“They do not address the underlying cause of obesity, which is the food environment. And until we change the food environment, we can’t expect that we’re going to reverse the obesity epidemic,” she said.
