Is all the weight regained?

No. In the STEP-1 extension about two-thirds returned within a year, and average weight remained below baseline, with nearly half of participants still at least 5% down.

How fast does regain happen?

Meta-analysis estimates put it at roughly 0.8 kg per month, with meta-regression suggesting a half-life around 23 weeks toward a maximum of about 75% of the loss.

Do the newer compounds solve this?

Not yet demonstrated. Maintenance studies are running across the class, including TRIUMPH-6 for retatrutide, and none had resolved the question at the time of writing.

GLP-1 & Incretin Science

What the Data Says About Weight Regain After Stopping

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-233 cited sources

In the STEP-1 extension, participants who stopped semaglutide after 68 weeks regained roughly two-thirds of the weight they had lost within one year, moving from 17.3% mean reduction to a net 5.6%. A 2026 meta-analysis of 37 studies estimated regain at approximately 0.8 kg per month after stopping semaglutide or tirzepatide.

Key facts

STEP-1 reduction at 68 weeks: 17.3% mean
Net reduction one year after stopping: 5.6%
Proportion of loss regained: About two-thirds
Meta-analysis regain rate: ~0.8 kg per month
Meta-regression maximum regain: 75.3%, half-life ~23 weeks
Still ≥5% below baseline at 1 year: Nearly half of participants

What the STEP-1 extension actually found

Participants in the STEP-1 extension had reached 17.3% mean weight reduction at 68 weeks on semaglutide. One year after treatment stopped, they had regained 11.6 percentage points, leaving a net reduction of 5.6% from baseline. That is roughly two-thirds of the loss returning within twelve months of cessation.

The part that gets omitted

Coverage of this finding usually stops at 'two-thirds regained', which is accurate but incomplete. Average weight remained below baseline a year after stopping, and nearly half of participants were still at least 5% below their starting weight. Regain was substantial and partial, not total, and the distribution matters as much as the mean.

What the meta-analyses add

A systematic review and nonlinear meta-regression across six randomised controlled trials estimated a maximum regain of 75.3% of lost weight, with a recovery rate constant corresponding to a half-life of about 23 weeks. Separately, a 2026 meta-analysis covering 37 studies and 9,341 people estimated regain of roughly 0.8 kg per month after stopping semaglutide or tirzepatide. The two approaches converge on the same picture: regain is predictable, gradual and incomplete.

Why this is the field's central unresolved question

Every compound in the pipeline reports its headline figure on treatment. None of them has resolved what happens after. This is why maintenance-dosing studies matter more than another few percentage points of peak reduction — TRIUMPH-6, registered as NCT06859268, is retatrutide's maintenance study, and equivalents exist across the class. Until those read out, peak reduction figures describe a state that has to be sustained rather than an outcome that has been achieved.

What it does not tell you

These are trial populations under trial conditions, and cessation in a trial is not the same as cessation in practice. The data describe what happened on average to specific cohorts; they are not a prediction for any individual and are not guidance about starting or stopping anything. That is a decision for a prescriber.

Extended research context

The GLP-1 & Incretin Science deep dive

Deep dive: the two routes to a bigger effect

Every compound trying to beat GLP-1 alone has taken one of two routes. The first adds more receptors from the same hormone family — GIP in tirzepatide, GIP and glucagon in retatrutide. The second adds a non-incretin satiety hormone, which in practice means amylin: CagriSema combines cagrilintide with semaglutide, and amycretin engages both receptors from one molecule. Both routes work, because they recruit signalling pathways that do not fully overlap. Neither has escaped the constraint that binds all of them, which is that gastrointestinal tolerability worsens as effect size grows.

Deep dive: why a percentage is not a result

The most-quoted numbers in this field are the least comparable. REDEFINE 1 reported 22.7% and 20.4% for the same compound in the same trial — the first among participants who adhered to treatment, the second across everyone randomised. TRIUMPH-1 reported 28.3% in an uncomplicated obesity population while TRIUMPH-3 reported up to 22.6% in adults with established cardiovascular disease, using the same compound. Before any two figures can be compared they have to match on estimand, population, duration, comparator and whether the number is placebo-adjusted. Most published comparisons match on none of them.

Deep dive: what happens after the trial stops

Every headline figure describes weight while treatment continues. The STEP-1 extension found that a year after semaglutide was stopped, participants had given back roughly two-thirds of what they lost, moving from 17.3% mean reduction to a net 5.6% — though average weight remained below baseline and nearly half stayed at least 5% down. Meta-analysis puts regain at around 0.8 kg per month. This is why maintenance studies such as TRIUMPH-6 matter more to the field's future than another two points of peak reduction.

Research applications

▸Comparing incretin and amylin compounds on a like-for-like basis
▸Interpreting estimands, thresholds and placebo-adjusted figures in trial reports
▸Tracking the obesity pipeline across sponsors and jurisdictions
▸Understanding receptor pharmacology behind GLP-1, GIP, glucagon and amylin
▸Distinguishing licensed medicines from investigational compounds

Handling checklist

✓Identify which estimand a quoted percentage comes from before citing it
✓Check the trial population and baseline BMI against the comparison you are making
✓Confirm the duration and whether the reduction curve had plateaued
✓Read discontinuation rates alongside efficacy figures
✓Verify every NCT identifier against ClinicalTrials.gov rather than secondary reporting

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Comparing headline percentages across different trials

Fix: Population, duration, estimand and comparator all differ; the numbers are not interchangeable.

✗ Quoting the larger of two figures from the same trial

Fix: Name the estimand. Efficacy and treatment-policy answer different questions.

✗ Treating peak reduction as a durable outcome

Fix: Substantial regain follows cessation across the class; peak figures describe a maintained state.

✗ Assuming an oral route means a weaker mechanism

Fix: Route and receptor count are independent. Orforglipron is weaker because it hits one receptor, not because it is a tablet.

✗ Reading investigational compounds as available treatments

Fix: Most of this pipeline holds no authorisation anywhere; mazdutide is approved only in China.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Is all the weight regained?: No. In the STEP-1 extension about two-thirds returned within a year, and average weight remained below baseline, with nearly half of participants still at least 5% down.
How fast does regain happen?: Meta-analysis estimates put it at roughly 0.8 kg per month, with meta-regression suggesting a half-life around 23 weeks toward a maximum of about 75% of the loss.
Do the newer compounds solve this?: Not yet demonstrated. Maintenance studies are running across the class, including TRIUMPH-6 for retatrutide, and none had resolved the question at the time of writing.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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