Eight weeks. That’s how long it takes, on average, for the pounds to begin creeping back after someone stops taking the world’s most promising weight-loss drugs.

Medications like semaglutide (Ozempic) and liraglutide have been hailed as “game-changers” in the fight against obesity, helping people shed 10, 15, even 20% of their body weight. But we don’t know as much about what happens when the prescription runs out. According to a new study published by researchers at Peking University People’s Hospital, there’s a big rebound effect.

In just a few years, weight-loss drugs like Ozempic and Wegovy have become a global sensation. They promise to do something millions of people dream of: rapid, effortless weight loss without surgery or starvation. Backed by dramatic trial results and viral celebrity endorsements, they’ve become so popular that 1 in 8 adults in the US have already taken them at some point.

Yet, as so often happens with weight loss, shedding extra pounds is one thing — keeping them off is another.

The team, led by endocrinologist Xiaoling Cai, analyzed 11 randomized controlled trials, tracking more than 2,400 adults who had taken FDA- or EMA-approved anti-obesity drugs. Their question was simple: What happens after the medication stops?

The simple answer is that the weight gradually crept back, though not entirely. On average, participants regained 1.5 kilograms (about 3.3 pounds) within eight weeks of stopping treatment. At twelve weeks, it was 1.8 kilograms. By twenty weeks, 2.5 kilograms. That might not sound like much. But it reveals a consistent trend, a steady reversal of the drug’s effects.

The weight stabilized after six months. It settles at a plateau, higher than the low point reached with the medication, but lower than where people started. The rebound effect wasn’t full, but it was definitely there.

The body is stubborn

For decades, researchers have known that the human body resists weight loss. When we lose fat, our levels of leptin (the hormone that signals fullness) fall. At the same time, ghrelin, the hunger hormone, rises. Our metabolism slows, our cravings grow more intense, and our bodies burn fewer calories even at rest. Recent studies have also shown that our cells have a “memory” and they try to push you back to a baseline weight.

In other words, our weight has more inertia than we thought. It’s a tug-of-war with physiology, and our physiology is stubborn.

GLP-1 drugs short-circuit some of those defenses. But once withdrawn, the body mounts a counterattack. It doesn’t forget where it started from and it tries, with impressive efficiency, to get back there. It’s important to keep in mind that it doesn’t revert quite to the baseline, but it doesn’t stay at the minimum weight either.

This study doesn’t say anti-obesity drugs don’t work. Quite the opposite: they work extremely well — while you’re on them.

But it does seem to show that these are short-term fixes. Like glasses for near-sightedness, their benefits vanish when you stop using them. For a chronic condition like obesity, that means we may need to think about these drugs as long-term treatments, perhaps lifelong ones. But this raises tough questions for doctors, patients, and policymakers. Should people stay on GLP-1 drugs indefinitely? Are they safe for long-term use? Who pays the bill, and what happens when access ends?

We keep misunderstanding obesity

The study also examined what happened when patients received lifestyle support like diet plans, exercise regimens, and coaching, either during or after drug therapy. Surprisingly, weight regain happened even when lifestyle interventions continued. That came as a surprise and runs counter to conventional wisdom.

It does show, however, that there’s much we still don’t understand about how our body deals with extra pounds. It also suggests we keep falling into the same obesity management traps.

Obesity is still too often framed as a personal failure. If you’re overweight, it’s your fault, a matter of weak will or bad choices. But studies like this underscore what obesity researchers have long argued: that weight regulation is mostly biological. It’s the result of complex feedback loops between the brain, gut, hormones, and fat tissue. Of course, all of this is overlaid on our modern lifestyle and often processed, unhealthy foods.

But the idea that people can simply ‘choose’ to be thin ignores how our bodies actually work. We’re not machines. We’re ecosystems, and ecosystems resist change.

The rebound problem doesn’t mean we’re stuck. Researchers are already testing combination therapies that pair GLP-1 drugs with other molecules to blunt hunger even more effectively. Perhaps, after a longer prescription period, the rebound effect would be slower.

This new generation of weight-loss drugs is promising. But they’re still just tools, not magic bullets. To make them work long-term, we may need to keep using them long-term.

The study “Trajectory of the body weight after drug discontinuation in the treatment of anti‑obesity medications” was published in the journal BMC Medicine. 10.1186/s12916-025-04200-0