The Weight Comes Back. What the Data Say About Life After GLP-1s.

The new obesity drugs work, but only while you take them. The evidence on stopping is now clear enough to change how we think about starting.

By Qais S. Dirar, MBBS, MPH, DrPH

For most of my career, the honest answer to "What works for obesity?" was a list of modest options and a shrug. That has changed. A generation of drugs built on the gut hormone GLP-1 now produces weight loss that once seemed possible only with surgery. And as millions of people start these medications, a quieter question is becoming the one I hear most: What happens when I stop?

The question is not academic. People stop for many reasons: cost, supply shortages, side effects, pregnancy, or simply the sense that the job is done. Over the past year, the evidence on what follows has matured from scattered trial extensions into something closer to a law of physiology. It deserves a clear reading.

How well the drugs work

Start with the benchmark. In SURMOUNT-5, published in the New England Journal of Medicine in 2025, 751 adults with obesity but without type 2 diabetes were randomly assigned to tirzepatide or semaglutide for 72 weeks. Those on tirzepatide lost an average of 20.2% of their body weight, and those on semaglutide lost 13.7%. Waist circumference fell by 18.4 and 13.0 centimetres respectively (NEJM, 2025).

Readers should know two things about that trial. It was open-label, meaning participants knew which drug they were receiving, and it was funded by tirzepatide's manufacturer. Neither fact makes the result wrong. Both are reasons to read it as one strong data point rather than the final word.

What stopping does

The more consequential evidence concerns what happens afterward. A 2025 systematic review and meta-analysis in eClinicalMedicine pooled 18 randomised trials covering 3,771 participants who were followed for at least 12 weeks after stopping a GLP-1 receptor agonist. Among people treated for obesity, stopping was followed by an average regain of 5.63 kilograms. HbA1c, a marker of long-term blood sugar, rose by 0.25 percentage points, and waist circumference, BMI, blood pressure and fasting glucose all worsened. Regain was larger with longer follow-up: 7.31 kilograms beyond 26 weeks, versus 2.51 kilograms at shorter intervals (eClinicalMedicine, 202500614-5/fulltext)).

In people with type 2 diabetes, the regain was smaller, about 2 kilograms, but HbA1c rose by roughly 0.65 percentage points. For patients who relied on these drugs for glucose control, that is a meaningful step backward.

The shape of the rebound

A single average hides the most useful finding: rebound follows a predictable curve. A second review in eClinicalMedicine, published in 2026, gathered 48 studies and modelled weight trajectories from six randomised trials with 3,236 participants. One year after stopping, people had regained 60% of the weight they lost on treatment. Projected forward, regain slowed and levelled off at about 75%, with a half-life of roughly 23 weeks (eClinicalMedicine, 2026).

Picture someone who lost 20 kilograms. On average, about 12 would return in the first year, and the total would settle at around 15. That person would still weigh less than before treatment. The benefit shrinks substantially, but it does not disappear. The authors rated most included studies at moderate risk of bias, and individual experience varies widely around these averages. Still, the direction is unmistakable, and so is the timing: the steepest regain comes in the first months.

The real world is harsher than the trial

Clinical trials keep people on their medication. Ordinary life does not. A 2025 retrospective study in Obesity followed 7,881 adults without diabetes who started semaglutide or tirzepatide in a large US health system. At one year, average weight loss was 11.9% among those who stayed on treatment, 6.8% among those who stopped between three and twelve months, and 3.6% among those who stopped within three months (Obesity, 2025). Most patients, 80.8%, were also on lower maintenance doses than the trials used. That gap between trial efficacy and real-world effectiveness is familiar to anyone who studies medicines in populations, and it is especially wide here.

Why the body pushes back

These drugs act on the hormonal signals that govern appetite and fullness. When the drug is withdrawn, those signals return, and the body's long-evolved defence of its previous weight reasserts itself. That is biology, not a failure of willpower. Treating regain as a personal failing misreads the science and does real harm to patients.

The better framing comes from how we manage hypertension or high cholesterol. No one is surprised when blood pressure rises after the pills stop. Obesity is a chronic, relapsing non-communicable disease. The evidence now asks us to treat it like one.

What this means for patients and clinicians

Several implications follow, and none of them requires taking a side in the culture war over these drugs.

Stopping should be a plan, not an event. Because regain comes early, the first six months after stopping deserve the closest attention: regular checks of weight, waist, blood pressure and glycaemic markers, agreed in advance with a clinician.

De-escalation deserves study. Whether tapering doses, using lower maintenance doses or treating intermittently can blunt the rebound is an open and important research question. Patients should discuss the options rather than stopping abruptly.

Lifestyle support still matters. Medication does not make diet, physical activity, sleep and strength training irrelevant. These are the supports that remain once the drug is gone.

Access is part of the science. If benefit lasts only as long as treatment does, then affordability and supply decide outcomes as much as pharmacology does. Health systems weighing coverage of these drugs should budget for long-term use, not a short course.

The bottom line

The headline is not that GLP-1 drugs fail. They are among the most effective medicines we have for a disease that has long resisted treatment. The lesson is that they treat obesity rather than cure it. Whoever starts one, and whoever pays for it, should plan for the long term from the first prescription.

This article summarises published research and is not medical advice. Please consult your own clinician before starting, changing or stopping any medication.

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Qais S. Dirar, MBBS, MPH, DrPH, is a physician and epidemiologist who writes about metabolic health, clinical evidence and health systems.