Everyone who starts a GLP-1 protocol should understand what happens when it stops.

A Bayesian re-analysis by Kow and colleagues, published in Endocrinology, Diabetes & Metabolism, synthesized 6 studies covering 10 treatment arms and 1,776 adults who discontinued semaglutide or tirzepatide. It's the most rigorous quantification yet of what the weight regain trajectory actually looks like after stopping these drugs.

Here's what it found — and where the data ends and the modeling begins.

The Numbers

Mean weight lost at time of cessation: 15.35 kg (95% CrI 11.18–19.60)

Monthly regain rate: 1.04 kg per month (95% CrI 0.80–1.29)

Modelled regain by 12 months: roughly 12.5 kg — about four-fifths of the weight lost; half of it back by about 7.5 months

Projected return to baseline weight: 15.0 months primary estimate (95% CrI 10.1–21.1); 17.3 months for semaglutide and 14.5 for tirzepatide in drug-specific models

Source: Kow CS, Thiruchelvam K, Ramachandram DS, Zaihan AF. "Weight Regain Trajectories After Discontinuation of Semaglutide or Tirzepatide: A Reconstructed Aggregate-Data Bayesian Longitudinal Meta-Analysis." Endocrinol Diabetes Metab. 2026;9(5):e70325. PMID 42673571. DOI 10.1002/edm2.70325.

The Critical Caveat Everyone Will Skip

The headline number — "return to baseline in about 15 months" — is a model projection, not a measured outcome.

Observed follow-up in the underlying studies ran to 52 weeks. Beyond 52 weeks, the analysis uses linear extrapolation to project when participants would return to baseline weight.

That projection may be directionally correct. It may also overestimate or underestimate the actual trajectory. It is not measured data beyond the one-year mark.

This distinction matters because "patients regain all their weight in 15 months" is a fundamentally different claim from "our model, extrapolated beyond our observed data window, projects a return to baseline at approximately 15 months."

Both are worth knowing. They carry different levels of certainty.

The finding that is well-supported by the observed data: weight regain after stopping semaglutide or tirzepatide is rapid and clinically meaningful within the first year — the BMJ meta-analysis of the same six studies measured 9.9 kg regained in the first year (0.8 kg per month). That's not a projection. That's what the studies measured.

How This Compares to Earlier Data

The Kow analysis re-models the incretin subset of a larger systematic review published in the BMJ in January 2026 (West et al.: 37 studies, 63 arms, 9,341 participants across all weight-management medications). For semaglutide and tirzepatide specifically — 10 arms, 1,776 participants, the same six studies — West and colleagues found 14.7 kg lost at cessation, 0.8 kg per month regained, 9.9 kg back within the first year, and a projected return to baseline at about 1.5 years. Cardiometabolic markers tracked back toward baseline within about 1.4 years.

A separate meta-analysis of 17 cessation studies (3,793 participants in cessation arms; Patel et al., Cureus, June 2026) reported pooled regain of 7.20% of body weight, 7.19% after semaglutide 2.4 mg and 13.04% after tirzepatide, and — in three comparative RCTs — cessation arms gaining 14.26 percentage points more than continuation arms.

Three analyses, three methods, one direction. The magnitude within the first year is measured; the precise trajectory beyond 52 weeks remains modelled.

Why Weight Comes Back: The Biology

The regain isn't a failure of willpower. It's a predictable consequence of how these drugs work.

GLP-1 receptor agonists reduce appetite by acting on satiety signaling in the brain and slowing gastric emptying. When you stop the drug, those signals return to pre-treatment levels. The underlying adiposity setpoint — the body weight your brain defends as "normal" — hasn't changed.

This is why every major obesity guideline now frames GLP-1 therapy as management of a chronic disease, not a cure. Stopping the drug is analogous to stopping blood pressure medication: the disease doesn't stop because the treatment stops.

The additional complication: lean mass lost during GLP-1 therapy. 26% of all weight lost on tirzepatide in the SURMOUNT-1 DXA substudy was lean tissue. When weight regains after stopping, it tends to return fat-preferentially. A patient who lost 40 lbs (10 lbs muscle, 30 lbs fat) and then regains 40 lbs may end up with less muscle and more fat than when they started — a net worsening of body composition despite equivalent scale weight.

What the Exit Requires — That Nobody Plans

The regain data reveals a structural gap in how GLP-1 programs are typically delivered.

Most programs have a clear on-ramp: assessment, prescription, titration schedule, regular weigh-ins. Almost none have a documented off-ramp: what happens when the patient stops, what the maintenance plan looks like, how to monitor for regain, how to preserve lean mass through cessation.

The drugs work while you take them. The question is what you build during the treatment window that persists after it.

Based on the evidence, the factors most likely to influence post-cessation outcomes:

1. Lean mass preserved during treatment Patients who maintain or build lean mass during GLP-1 therapy have a higher resting metabolic rate, which partially offsets regain. Resistance training during treatment is the primary tool for this.

2. Behavioral infrastructure built during treatment The appetite suppression window is an opportunity to build eating and exercise habits with less friction than normal. Whether patients use that window productively affects what happens when the drug stops.

3. Monitoring after cessation The regain data shows that most of the weight comes back within the first year after stopping. Without systematic monitoring in that window — body composition, not just scale weight — clinicians and patients are flying blind during the highest-risk period.

4. Transition planning For some patients, indefinite continuation of GLP-1 therapy is the most evidence-consistent plan. For others, a lower-dose maintenance strategy or transition to a different approach is appropriate. The point is that cessation should be planned, not just happened-upon.

The Measurement Gap

The regain data makes one thing clear: the outcomes that matter most happen over years, not months.

A patient who loses 15 kg over 68 weeks, regains 10 kg in the following 12 months, and ends up 5 kg below their starting weight after 2.5 years has a very different clinical picture than one who loses 15 kg and maintains it. Current standard-of-care monitoring rarely captures that trajectory systematically.

This is the argument for longitudinal tracking that doesn't stop when the prescription does.

Body composition at baseline, during treatment, at cessation, and at 6-month intervals after stopping — that's the data set that actually tells you whether GLP-1 therapy produced a durable outcome. Scale weight alone misses the lean mass picture. A single measurement misses the trajectory.

The exit is the part nobody plans for. It's the part the tracking layer is built for.

→ Track your protocol at PeptidesGPT.com

Sources:

Kow CS, Thiruchelvam K, Ramachandram DS, Zaihan AF. "Weight Regain Trajectories After Discontinuation of Semaglutide or Tirzepatide: A Reconstructed Aggregate-Data Bayesian Longitudinal Meta-Analysis." Endocrinol Diabetes Metab. 2026;9(5):e70325. PMID 42673571. DOI 10.1002/edm2.70325.
West S, Scragg J, Aveyard P, et al. "Weight regain after cessation of medication for weight management: systematic review and meta-analysis." BMJ. 2026;392:e085304. PMID 41500720. DOI 10.1136/bmj-2025-085304.
Patel H, Babli SA, et al. "Post-cessation Weight Regain After Weight Management Medications: A Systematic Review and Meta-Analysis." Cureus. 2026;18(6):e111786. PMID 42534203. DOI 10.7759/cureus.111786.
Look M, et al. SURMOUNT-1 body composition substudy. Diabetes Obes Metab. 2025;27(5):2720–2729. PMID 39996356. DOI 10.1111/dom.16275.

PeptidesGPT is an educational platform. This content is for informational purposes only and does not constitute medical advice. Decisions about continuing, stopping, or changing GLP-1 therapy should be made with a licensed healthcare provider.

What Happens When You Stop: The Real Weight Regain Data After GLP-1 Therapy