STEP-1 Extension Trial: A Plain-English Overview of What It Established

At a glance

| Parameter | Detail | |-----------|--------| | N | 327 (from original STEP-1 cohort of 1,961) | | Intervention | Semaglutide 2.4 mg/week for 68 weeks, then withdrawal and 1-year follow-up | | Comparator | Same participants served as their own controls (on-treatment vs. off-treatment periods) | | Duration | 68-week treatment + 52-week off-treatment extension (120 weeks total) | | Primary endpoint | Change in body weight from week 68 to week 120 | | Key result | Mean weight regain of 11.6 percentage points after stopping; net loss from baseline only ~5.6% at week 120 vs. ~17.3% at week 68 |

The Question This Trial Asked

The original STEP-1 trial demonstrated that once-weekly semaglutide 2.4 mg produced an average 14.9% body weight reduction over 68 weeks. The extension study asked the obvious next question: what happens when you stop?

Clinicians and patients had long debated whether GLP-1 receptor agonists could "reset" body weight to a new set point. If they could, a finite treatment course might be sufficient. If they could not, stopping would simply invite the weight back. The STEP-1 Extension was designed to answer this directly by following a subset of completers for an additional year without the drug.

Who Was Enrolled

The 327 participants in the extension came from the original STEP-1 population. Eligibility for the parent trial required a BMI of 30 or above (or 27 with at least one weight-related comorbidity), age 18 and older, and no type 2 diabetes diagnosis. The extension cohort was drawn from a single-country subset (all U.S.-based sites) willing to continue follow-up visits after unblinding.

Key baseline characteristics of the extension subgroup mirrored the full STEP-1 population: mean age approximately 46 years, roughly 74% female, mean baseline BMI around 38 kg/m². These were adults with significant obesity who had already demonstrated adherence by completing the 68-week treatment phase.

What They Were Given (and Then Taken Away)

During the first 68 weeks, participants received subcutaneous semaglutide 2.4 mg once weekly alongside lifestyle counseling (reduced-calorie diet, 150 minutes/week physical activity). The dose was escalated over 16 weeks following the standard titration schedule: 0.25 mg for 4 weeks, 0.5 mg for 4 weeks, 1.0 mg for 4 weeks, 1.7 mg for 4 weeks, then the maintenance dose of 2.4 mg.

At week 68, the drug was discontinued. Participants received no pharmacotherapy during the 52-week off-treatment extension. Lifestyle counseling continued, but adherence to exercise and dietary recommendations was self-directed without active intervention support.

This design created a clean before-and-after comparison within the same individuals, eliminating many confounders that plague between-group analyses of weight maintenance.

What Was Measured

The primary outcome was the change in body weight (%) from week 68 (end of treatment) to week 120 (end of off-treatment follow-up). Secondary outcomes included changes in waist circumference, systolic and diastolic blood pressure, fasting glucose, HbA1c, fasting lipids, and C-reactive protein over the same interval.

The investigators also tracked the proportion of participants who maintained clinically meaningful weight loss thresholds (5%, 10%, 15%, and 20% from baseline) at week 120 versus week 68.

What Was Found

Weight Regain

The results were unambiguous. From the published data:

| Timepoint | Mean Weight Change from Baseline | |-----------|----------------------------------| | Week 68 (end of semaglutide) | −17.3% | | Week 120 (1 year off drug) | −5.6% | | Regain from week 68 to 120 | +11.6 percentage points |

In absolute terms, participants lost an average of 17.3 kg on treatment and regained 11.6 kg after stopping. The net retained loss of approximately 5.6% from original baseline was still statistically greater than zero, but clinically far less impressive than the on-treatment result.

Threshold Analysis

The proportion maintaining various weight-loss thresholds collapsed:

| Threshold | At Week 68 | At Week 120 | |-----------|-----------|-------------| | ≥5% loss | 90.4% | 48.6% | | ≥10% loss | 75.2% | 26.8% | | ≥15% loss | 55.8% | 11.6% | | ≥20% loss | 34.8% | 5.4% |

Fewer than half of participants maintained even a 5% weight loss one year after discontinuation. Only about 1 in 9 kept 15% or more off.

Cardiometabolic Reversal

The metabolic improvements tracked weight closely. Waist circumference, which had decreased by approximately 13.5 cm at week 68, returned to only 4.8 cm below baseline by week 120. Systolic blood pressure, triglycerides, and CRP all followed similar trajectories of partial or near-complete reversal. The biological message was consistent: the metabolic benefits of semaglutide were drug-dependent, not permanently "locked in" by the weight loss itself.

Methodology Notes Beyond the Abstract

Several design features strengthen (or complicate) interpretation:

Single-arm extension, not randomized withdrawal. The off-treatment period was observational. There was no randomized arm that continued semaglutide for comparison during weeks 68 to 120. This means we cannot calculate, from this dataset alone, how much weight participants would have continued to lose (or maintain) had they stayed on drug. The STEP-4 trial later addressed this with a randomized withdrawal design and found similar regain patterns.

Subset selection. The 327 participants were drawn from U.S. sites only and had to consent to extended follow-up. This introduces potential selection bias: these may have been more motivated individuals, which would make the regain findings, if anything, an underestimate of what happens in typical clinical populations.

No active lifestyle intervention intensification. Participants were told to maintain diet and exercise habits, but no structured program was provided during the off-treatment year. This mirrors real-world scenarios where patients stop medication without a formal maintenance plan.

Missing data handling. The investigators used a mixed model for repeated measures (MMRM) as the primary analysis approach, which assumes data are missing at random. Given that participants who regained more weight may have been more likely to drop out of follow-up visits, the reported regain could be slightly conservative.

What the Authors Acknowledged as Limitations

The publication explicitly noted:

1. The extension cohort was a convenience subset, not prespecified as part of the original randomization.
2. Without a continued-treatment arm, the study cannot distinguish between true pharmacologic withdrawal effect and natural weight trajectory.
3. Lifestyle adherence was not objectively measured during the off-treatment period.
4. The 52-week follow-up, while informative, does not tell us whether regain stabilizes, continues, or reverses at longer timeframes.

Clinical Translation: What This Means for Practice

The STEP-1 Extension did not discover something new about weight biology. Clinicians who treated obesity with older medications (phentermine, orlistat) already knew that weight returns after drug cessation. What this trial accomplished was quantifying the magnitude and speed of regain with a highly effective modern agent, in a well-characterized population, with rigorous follow-up.

The practical implications shaped subsequent prescribing patterns and guideline recommendations:

Indefinite treatment framing. The 2022 American Gastroenterological Association guideline on anti-obesity medications explicitly cited discontinuation data when recommending long-term pharmacotherapy for patients who respond to GLP-1 agonists. The analogy to antihypertensives became standard: you do not stop blood pressure medication because your blood pressure normalized.

Insurance and access battles. Payers who imposed 6-month or 12-month treatment limits faced pushback from clinicians armed with this data. If stopping reliably causes regain, arbitrary time limits create a medically counterproductive cycle of loss and regain.

Patient counseling. The data gave clinicians concrete numbers for informed consent conversations. Rather than vague warnings about "some weight may return," prescribers could say: expect to regain approximately two-thirds of what you lost if you stop without an alternative strategy.

Dose-reduction research. The completeness of regain motivated subsequent studies examining whether lower maintenance doses (rather than full cessation) could preserve benefits while reducing cost and side-effect burden.

Placing This Trial in Context

The STEP-1 Extension was not the only semaglutide withdrawal study. STEP-4 used a randomized design where all participants received semaglutide for 20 weeks, then were randomized to continue or switch to placebo for 48 additional weeks. The placebo-switch group regained while the continuation group lost additional weight, confirming the STEP-1 Extension findings in a more rigorous framework.

Tirzepatide discontinuation data from SURMOUNT-4 showed a near-identical pattern: substantial regain after stopping the dual GIP/GLP-1 agonist, reinforcing that this is a class-wide phenomenon rather than semaglutide-specific.

Together, these trials established the scientific foundation for treating obesity as a chronic, relapsing condition requiring ongoing pharmacologic management in patients who respond to GLP-1-based therapies.

Frequently asked questions

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References

1. Wilding JPH, Batterham RL, Davies M, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553-1564. PubMed

2. Rubino D, Abrahamsson N, Davies M, et al. Effect of continued weekly subcutaneous semaglutide vs placebo on weight loss maintenance in adults with overweight or obesity: The STEP 4 randomized clinical trial. JAMA. 2021;325(14):1414-1425. PubMed

3. Aronne LJ, Sattar N, Horn DB, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity: The SURMOUNT-4 randomized clinical trial. JAMA. 2024;331(1):38-48. PubMed

4. Novo Nordisk. Wegovy (semaglutide) injection prescribing information. U.S. Food and Drug Administration. FDA Label

5. Grunvald E, Shah R, Engel S, et al. AGA clinical practice guideline on pharmacological interventions for adults with obesity. Gastroenterology. 2022;163(5):1198-1225. PubMed