
22/05/2024
Weight-suppressant drugs have helped millions to lose weight. But once they're stopped, people tend to regain most of what they shed. What does this mean for their long-term health?
As director of the Washington Centre for Weight Management and Research, Domenica Rubino has become frustrated with growing perceptions over the last three years that weight loss drugs such as Novo Nordisk's Ozempic and Wegovy, and Eli Lilly's Mounjaro, are permanent cures for obesity.
"Obesity is not like an infection where you take antibiotics and you're done," says Rubino, sighing. "It's not any different than hypertension or diabetes or the many other chronic illnesses that we deal with, where you have to use chronic medication."
For over the past three years, the arrival of a new class of drugs known as GLP-1 agonists, so-called for their ability to mimic the action of the natural GLP-1 gut hormone that promotes satiety, has transformed the weight-loss field.
Initially, the US Food and Drug Administration approved Wegovy, the brand name for a GLP-1-based medicine called semaglutide, for chronic weight management in June 2021. The insatiable demand saw Mounjaro or tirzepatide arrive at the end of 2023 and now a newer, reportedly more effective drug called retatrutide is in the pipeline.
There is no question that GLP-1 drugs are effective at helping people lose weight. A landmark clinical trial of semaglutide, published in 2021, found that participants experienced an average of 15% weight loss over the course of 68 weeks while those on placebo lost 2%. Some of those taking the drug, however, shed as much as 20% of their starting weight. The purported health benefits now appear to be even more far-reaching, with the latest data from a trial called Select, published in 2023, showing that semaglutide can slash the risk of heart attacks and strokes by a fifth in patients with an existing history of cardiovascular disease.
But given their high prices – a month's supply of Wegovy costs $1,350 (£1,062) – and onerous side effects which can include nausea, stomach pain and heartburn, the question has always been, what happens when people stop taking them?
Various studies have attempted to examine this particular question, and all seem to point to the same answer – the pounds swiftly pile back on. In one trial, around 800 people received weekly semaglutide injections accompanied by dietary adjustments, a prescribed exercise regime and psychological counselling, all of which helped them to lose nearly 11% of their starting weight over four months. But when a third of the participants were subsequently switched to a placebo injection for another year, they regained 7% of the lost weight.
The same trend was seen after the 2021 trial, known as Step 1. After 68 weeks of semaglutide injections, the average patient lost more than 15% of their body weight, but within 12 months of treatment ending, patients regained two thirds of their prior weight loss on average. This was associated with a similar level of reversion to the patients' original baselines in some markers of their cardiometabolic health – a category which includes conditions such as diabetes and heart attacks.
Both Rubino and other experts around the world have seen similar patterns when administering GLP-1 drugs in their clinics. "There will be a small proportion of people, 10% maximum, that are able to maintain [all] the weight they've lost," says Alex Miras, a clinical professor of medicine at Ulster University.
The trajectory of weight regain is typically faster than the time it takes people to lose the weight in the first place, according to Miras. "People put most of it back on in the first three to six months," he says.
Miras and others are keen to emphasise that this could have been expected. For all chronic illnesses, from rheumatoid arthritis to asthma to high blood pressure, patients usually relapse as soon as their treatment stops. But understanding why this happens with semaglutide, tirzepatide and other GLP-1 drugs could be crucial to understanding their longer-term health consequences and how best to prescribe them in future.