What the STEP 1 trial extension tells us about semaglutide, weight loss, and what happens when treatment stops

The numbers from the STEP 1 extension: how much weight came back, and how fast

The original STEP 1 trial ran for 68 weeks. Participants on semaglutide 2.4mg lost an average of around 15% of their body weight during that period. When the trial ended, a subset continued into a one-year observational extension (without the medicine, without intensive lifestyle support) to see what happened.

The answer was unambiguous. By the end of that extra year (week 120), participants had regained approximately two-thirds of the weight they had lost. Average body weight was sitting around 5.6% below the starting point, compared with the 14.9% reduction at the end of active treatment. The gap closed fast: much of the regain happened in the first 20 weeks after stopping. Improvements in waist circumference, blood pressure, fasting glucose and cholesterol followed a similar pattern — gains that had taken 68 weeks to achieve unwound in a fraction of that time.

It is worth reading the full Wegovy trial results picture alongside this, because the extension data does not undermine what semaglutide achieves during treatment. It sharpens the question of what happens after. You can also see how semaglutide's trial outcomes compare more broadly on our semaglutide results page.

Why weight comes back: the biology behind the STEP 1 withdrawal findings

The regain is not a failure of willpower. It reflects how GLP-1 receptor agonists work. Semaglutide slows gastric emptying, reduces appetite signals in the brain, and alters the hormonal environment around hunger. When treatment stops, those effects stop too. The body's own hunger hormones (ghrelin among them) reassert themselves, and the reduced appetite that felt manageable on treatment no longer has pharmaceutical support.

Obesity itself involves chronic dysregulation of these same hormonal pathways, which is why the STEP 1 extension findings mirror what researchers have seen after other weight-loss interventions. The medicine was addressing an ongoing biological process. Weight regain after semaglutide withdrawal is not unusual, it is the expected outcome when the treatment that was managing a chronic condition is removed.

This framing matters practically: it means the decision about stopping or continuing semaglutide is a clinical one, not a personal milestone. How quickly weight returns after stopping semaglutide depends on individual factors, but the STEP 1 data suggests the process begins promptly.

What the STEP 1 extension data means for the decision you are actually facing

You are probably reading this because you are trying to decide something: whether to start, whether to stop, whether continuing indefinitely is realistic, or whether what you have read about the STEP 1 withdrawal extension changes the calculation. That is a reasonable place to be.

The evidence supports treating semaglutide as a long-term medicine for a long-term condition, in the same way you would think about treatment for hypertension or high cholesterol. Stopping may be appropriate for a range of clinical reasons (pregnancy planning, surgery, a change in your health picture) but the STEP 1 extension data makes clear that doing so usually means accepting the likelihood of weight returning. Strategies to slow that process, such as sustained dietary changes and activity habits built during treatment, can make a difference. Practical approaches to protecting the progress made on Wegovy after stopping are worth understanding in advance.

On the NHS, NICE's appraisal of semaglutide (Wegovy) currently sets a maximum treatment duration of two years within specialist services. That ceiling does not apply to all clinical scenarios, and private prescribing decisions are made on individual assessment. If you want to understand your own position, the most direct route is a conversation with a clinician who can look at your full picture, not just the trial average. Speak to our prescribers through a free consultation to explore whether semaglutide is appropriate for you and what a realistic plan looks like. There is also broader context on weight management approaches on our weight loss treatments overview.

The practical question: long-term treatment versus a defined course

The STEP 1 extension study does not tell you whether to stay on semaglutide. It tells you what the alternative typically looks like. Some people will reach their goals, build lasting habits, and manage well after stopping. Others will find the weight returning quickly and the hunger harder to control. Both outcomes happen; the trial average does not determine your individual result.

What the data argues strongly against is treating semaglutide as a short course with a fixed end date decided arbitrarily. If you are on treatment and thinking about stopping, the question to answer with your prescriber is: what is the clinical reason, and is there a plan for what comes after? How long Wegovy takes to produce meaningful results is one part of that conversation; the exit strategy is another part that often gets less attention. The original STEP 1 paper in the New England Journal of Medicine and the extension data together give clinicians the clearest picture yet of both sides of that calculation.