STEP-1 Extension Data and What Happened After the Trial Ended

At a glance

| Detail | Value | |---|---| | Trial | STEP-1 (NCT03548935) | | N | 1,961 randomized (1,306 semaglutide, 655 placebo) | | Intervention | Semaglutide 2.4 mg subcutaneous once weekly | | Comparator | Matching placebo, both arms with lifestyle intervention | | Duration | 68 weeks on-treatment + off-treatment extension to week 120 | | Primary endpoint | Percent change in body weight at week 68 | | Key result | -14.9% semaglutide vs -2.4% placebo at week 68; two-thirds of weight regain by week 120 after discontinuation |

Why the Extension Data Matters More Than the Headline

The original STEP-1 publication made international headlines with its 14.9% mean weight loss figure. That number told clinicians what semaglutide could do over 68 weeks. It did not tell them what happens when a patient stops.

The STEP-1 trial extension, published by Wilding et al. in 2022, followed a subset of participants for an additional year after treatment withdrawal. This off-treatment phase was not an afterthought. It was pre-specified in the protocol, and it answered the question every prescriber and patient eventually asks: is this permanent?

The answer was unambiguous. Weight came back. So did the metabolic risk factors that had improved during active treatment.

Trial Design: The Off-Treatment Extension

The STEP-1 trial randomized adults with BMI ≥30 (or ≥27 with at least one weight-related comorbidity) to weekly subcutaneous semaglutide 2.4 mg or placebo for 68 weeks. Both groups received monthly lifestyle counseling. At week 68, all treatment stopped.

A total of 327 participants from the semaglutide group and 166 from the placebo group continued into the off-treatment extension, with follow-up assessments at weeks 88, 104, and 120. The extension cohort was not re-randomized. Participants simply stopped injections and continued lifestyle counseling alone.

Key design points that matter for interpretation:

• No taper. Semaglutide was discontinued abruptly at week 68, not gradually reduced. This mirrors real-world scenarios where insurance denial or supply disruption forces sudden cessation.
• Lifestyle counseling continued. Both groups maintained the same behavioral support, isolating the pharmacologic effect of drug withdrawal.
• Selection bias is real. The extension cohort skewed toward participants who had completed the full 68 weeks, meaning they were likely more adherent and motivated than the average enrollee.

Weight Regain: The Core Finding

By week 120 (one year after stopping semaglutide), participants in the former semaglutide group had regained approximately two-thirds of the weight they lost during the active treatment phase.

| Timepoint | Semaglutide group mean weight change from baseline | Placebo group mean weight change from baseline | |---|---|---| | Week 68 (end of treatment) | -14.9% | -2.4% | | Week 120 (1 year off-treatment) | -5.6% | -0.1% |

The trajectory was consistent and steady. Weight regain did not plateau at some partial recovery point. It followed a near-linear upward slope from weeks 68 to 120, suggesting that without continued pharmacologic appetite suppression, the biological drivers of weight regain, including adaptive thermogenesis and hormonal counter-regulation, reasserted themselves.

The semaglutide group still weighed less at week 120 than at baseline (roughly -5.6%), but the gap between the drug and placebo arms narrowed from 12.5 percentage points to approximately 5.5.

Cardiometabolic Parameters: They Reversed Too

Weight was not the only thing that bounced back. The STEP-1 trial had documented improvements across multiple cardiometabolic markers during active treatment. The extension showed most of these gains eroding after discontinuation.

| Parameter | Improvement at week 68 (semaglutide vs placebo) | Status at week 120 | |---|---|---| | Waist circumference | -13.5 cm vs -4.1 cm | Largely reversed | | Systolic blood pressure | -6.2 mmHg vs -1.1 mmHg | Partially reversed | | CRP (inflammation marker) | -55% vs -12% | Substantially reversed | | HbA1c (non-diabetic cohort) | -0.45% vs -0.15% | Reversed toward baseline | | Triglycerides | Improved | Partially reversed | | HDL cholesterol | Improved | Partially reversed |

The pattern was not identical across all markers. Blood pressure showed some residual benefit at week 120, possibly because even modest residual weight loss (<6%) provides some hemodynamic advantage. CRP, by contrast, tracked weight closely and returned to near-baseline levels, consistent with the inflammatory burden of regained adipose tissue.

What the Extension Did Not Measure

The STEP-1 extension had meaningful limitations that clinicians should weigh:

1. No cardiovascular event data. STEP-1 was a weight-loss efficacy trial, not a cardiovascular outcomes trial. The SELECT trial (Lincoff et al., NEJM 2023) later showed a 20% reduction in major adverse cardiovascular events with semaglutide 2.4 mg, but that was a separate study in patients with established cardiovascular disease.

2. No body composition detail. The extension tracked total body weight but did not report dual-energy X-ray absorptiometry (DXA) or other body composition data. The proportion of regained weight that was fat mass versus lean mass remains unknown from this dataset.

3. Small extension cohort. Only 327 of the original 1,306 semaglutide participants entered the extension. Completers may not represent the full trial population, and the selection effect likely biases toward better outcomes than the average discontinuer would experience.

4. No re-treatment arm. The extension did not test what happens if patients restart semaglutide after a gap. Whether efficacy is preserved, diminished, or enhanced on re-initiation was not addressed.

How These Data Shaped Clinical Practice

The STEP-1 extension results had direct consequences for how semaglutide reached patients.

FDA labeling. The Wegovy prescribing information describes semaglutide 2.4 mg as chronic therapy for weight management. The extension data provided the evidentiary basis for this framing. A drug that loses its effect upon discontinuation, by definition, requires continuous use to maintain benefit.

Insurance and prior authorization. Payers initially treated GLP-1 agonists for obesity as time-limited prescriptions (e.g., 6 or 12 months). The extension data undercut that model. Professional societies including the American Association of Clinical Endocrinology (AACE) and the Obesity Medicine Association (OMA) cited these findings when arguing that coverage denials based on arbitrary time limits are clinically inappropriate.

Patient counseling. The extension reframed the conversation between providers and patients. Semaglutide is not a course of treatment like an antibiotic. It functions more like a statin or antihypertensive: effective while taken, with recurrence of the underlying condition upon cessation.

Context From Other STEP Extension and Follow-Up Data

STEP-1 was not the only trial in the STEP program to examine durability. The STEP-4 trial (Rubino et al., JAMA 2021) used a withdrawal design where all participants received semaglutide for 20 weeks, then were randomized to continue or switch to placebo. Those switched to placebo regained 6.9% of body weight over the subsequent 48 weeks, while those continuing semaglutide lost an additional 7.9%. The separation between arms was stark and consistent with STEP-1 extension findings.

The STEP-5 trial extended active treatment to 104 weeks and showed that weight loss was maintained at approximately -15.2% for the full duration. This confirmed that the drug's efficacy does not wane with prolonged use, though it also confirmed that the effect is entirely dependent on continued dosing.

Taken together, the STEP program established two facts with high confidence: semaglutide 2.4 mg produces durable weight loss for as long as it is taken, and weight returns when it is stopped.

What We Still Do Not Know

Several clinically important questions remain unresolved by the existing STEP extension data:

• Dose reduction for maintenance. Could a lower dose (e.g., 1.0 mg weekly) preserve weight loss with fewer side effects and lower cost? No randomized data exist for this strategy with semaglutide 2.4 mg specifically, though real-world use of lower maintenance doses is common.

• Intermittent dosing. Some patients cycle on and off GLP-1 agonists due to cost, side effects, or personal preference. Whether intermittent use produces net benefit over years is unknown.

• Decade-scale outcomes. The longest controlled data for semaglutide 2.4 mg extend to approximately two years. Obesity is a lifelong condition. The gap between two years and twenty years of data is enormous.

• Predictors of regain velocity. Some STEP-1 extension participants regained weight faster than others. Identifying baseline characteristics (metabolic rate, hormonal profiles, genetic markers) that predict rapid regain could allow targeted intervention before weight returns.

Frequently asked questions

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References

• Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity. N Engl J Med. 2021;384(11):989-1002. PubMed
• 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
• 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
• Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221-2232. PubMed
• Wegovy (semaglutide) prescribing information. Novo Nordisk. Revised 2023. FDA Label
• Sumithran P, Prendergast LA, Delbridge E, et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011;365(17):1597-1604. PubMed