STEP-5 Extension Data and What Happened After the Trial Ended

At a glance

Parameter	Detail
N	304 (semaglutide 152, placebo 152)
Intervention	Semaglutide 2.4 mg subcutaneous once weekly
Comparator	Matching placebo injection + lifestyle intervention
Duration	104 weeks (the longest primary endpoint in the STEP program)
Primary endpoint	Percent change in body weight from baseline to week 104
Key result	-15.2% semaglutide vs -2.6% placebo (estimated treatment difference -12.6 percentage points, p<0.001)

Why STEP-5 Was Designed Differently

Most obesity drug trials run 52 to 68 weeks. That timeframe answers one question: does it work? It leaves a more important question unanswered: does it keep working?

STEP-5 was purpose-built as the durability arm of the broader STEP program. Novo Nordisk designed it with 104 weeks of continuous dosing to capture whether weight loss plateaued, reversed, or continued creeping downward over a second year. The trial enrolled adults with BMI ≥30 (or ≥27 with at least one weight-related comorbidity) at 41 sites across the United States, Canada, and Europe. Unlike STEP-1, which showed impressive results at 68 weeks, STEP-5 extended observation by 36 additional weeks on treatment.

The design also embedded a secondary question about cardiometabolic markers: do improvements in waist circumference, HbA1c, lipids, and blood pressure persist proportionally to weight loss, or do they plateau earlier?

The Weight-Loss Trajectory Over Two Full Years

The weight-loss curve in STEP-5 shows a pattern that carries real clinical meaning. Participants lost weight rapidly through weeks 0 to 60, then entered a plateau phase from approximately week 60 through week 104. The final 44 weeks showed neither meaningful additional loss nor regain while on therapy.

HealthRX.com Durability Framework: The Three Phases of GLP-1 Weight Response

This three-phase pattern is clinically useful because it tells prescribers what to tell patients: expect the scale to stop moving around month 14-15, and that is not failure. The drug is still preventing regain.

Key Efficacy Outcomes at Week 104

Over one-third of participants on semaglutide lost 20% or more of their starting weight at two years. That threshold was previously associated only with bariatric surgery.

What Happens When Semaglutide Stops: The STEP-1 Extension

STEP-5 itself did not include a post-treatment washout period. Participants who completed 104 weeks were on drug through the final visit. To understand what happens after cessation, we must look at the STEP-1 extension study (Wilding et al., Diabetes Obes Metab 2022), which followed participants for one year after stopping semaglutide at week 68.

The findings were stark:

Participants regained approximately two-thirds of their lost weight within 52 weeks of discontinuation. The cardiometabolic improvements (systolic blood pressure, triglycerides, CRP) followed the weight back up, though HbA1c showed somewhat more durability than other markers.

The Clinical Interpretation: Chronic Disease, Chronic Treatment

These data together tell a coherent story. STEP-5 demonstrates that two years of continuous semaglutide holds weight at a new, lower steady-state. The STEP-1 extension demonstrates that removing the drug allows the underlying pathophysiology to reassert itself within months.

This parallels what clinicians already accept for hypertension, type 2 diabetes, and hyperlipidemia: stopping the medication does not cure the condition. The 2022 AGA clinical practice guideline on pharmacological interventions for adults with obesity explicitly recommends long-term (potentially indefinite) pharmacotherapy when the medication is effective and tolerated, citing this exact evidence base.

The FDA label for Wegovy (semaglutide 2.4 mg) does not specify a treatment duration endpoint. The prescribing information states the drug is intended for "chronic weight management" alongside reduced-calorie diet and increased physical activity.

Safety Signals Over 104 Weeks

Two years of continuous exposure provided a more complete safety picture than shorter trials. The adverse event profile in STEP-5 was consistent with the GLP-1 receptor agonist class, but time-on-drug revealed some patterns:

The key safety finding from 104 weeks: no new signal classes emerged in the second year. Gastrointestinal events front-loaded in the titration phase (weeks 0-16) and largely attenuated. The gallbladder signal (cholelithiasis) is a class effect tied to rate of weight loss rather than drug mechanism specifically.

Pancreatitis occurred in 1 participant on semaglutide (0.7%) and 0 on placebo. Thyroid C-cell events (the theoretical rodent signal) were not observed. No cases of medullary thyroid carcinoma were reported.

Limitations the Authors Acknowledged

The STEP-5 investigators were explicit about several constraints:

1. Population homogeneity. The trial enrolled predominantly White participants (86.2%) from high-income countries. Generalizability to other populations remains an assumption, not demonstrated.

2. No post-treatment follow-up within STEP-5 itself. The protocol ended at week 104 with participants still on drug. The withdrawal question must be answered by cross-referencing other STEP trials.

3. Sample size. N=304 is adequate for efficacy estimation but underpowered for rare safety events. Pancreatic, thyroid, and cardiovascular signals require the larger N of SELECT (N=17,604) or post-marketing surveillance.

4. Lifestyle co-intervention. All participants received counseling on a 500 kcal/day deficit and 150 min/week physical activity. Disentangling drug effect from behavioral effect at the individual level is not possible from this design.

5. Open-label awareness. Though the trial was double-blind, significant GI side effects may have functionally unblinded some participants, potentially amplifying behavioral effort in the active arm.

Placing STEP-5 in the Broader STEP Program

STEP-5's unique contribution is confirming that the ~15% loss seen at 68 weeks in STEP-1 holds steady through 104 weeks. The effect does not wane. Combined with STEP-4's withdrawal data (rapid regain when switched to placebo at week 20), the program paints a complete picture: initiate, maintain, do not stop.

What SELECT Added After STEP-5

The SELECT cardiovascular outcomes trial (Lincoff et al., NEJM 2023, N=17,604) provided the cardiovascular endpoint data that STEP-5 was never powered to address. SELECT demonstrated a 20% reduction in major adverse cardiovascular events (MACE) with semaglutide 2.4 mg over a mean follow-up of 39.8 months. This extended the clinical rationale for long-term treatment from "weight maintenance" to "cardiovascular risk reduction," strengthening the case that indefinite therapy may be warranted in high-risk patients.

Clinical Translation: What Prescribers Should Take From This

The combined STEP-5 plus extension data support several practical conclusions:

• Set patient expectations at treatment initiation. Weight loss will plateau around month 14-15. That plateau represents success, not resistance.
• Plan for indefinite treatment. Stopping semaglutide after achieving target weight is, based on available data, likely to result in regaining two-thirds of lost weight within one year.
• Monitor gallbladder symptoms during rapid-loss phase (first 6-8 months) rather than during maintenance.
• GI tolerability improves substantially after the titration period. Patients who tolerate the first 16-20 weeks are unlikely to develop new GI intolerance in year two.

Frequently asked questions

›How long did STEP-5 participants stay on semaglutide?

Participants received semaglutide 2.4 mg (or placebo) continuously for 104 weeks (two full years). This made STEP-5 the longest-duration trial in the STEP program's primary publication set.

›Did participants regain weight while still taking semaglutide in STEP-5?

No. Weight remained stable at approximately -15% from baseline between weeks 60 and 104. The plateau represents a new steady-state, not the beginning of regain. Regain occurs after discontinuation, not during continued use.

›What happens when you stop semaglutide after long-term use?

The STEP-1 extension study showed that participants regained roughly two-thirds of their lost weight within one year of stopping semaglutide. Cardiometabolic improvements (blood pressure, triglycerides, waist circumference) also reversed proportionally.

›Is semaglutide meant to be taken indefinitely for weight loss?

Current FDA labeling and AGA guidelines support long-term (potentially indefinite) use for chronic weight management when the medication is effective and tolerated. No treatment duration cap is specified in the Wegovy prescribing information.

›Were there new safety concerns in the second year of STEP-5?

No novel safety signals emerged in year two. Gastrointestinal side effects were predominantly concentrated in the first 20 weeks during dose titration. The safety profile at 104 weeks was consistent with the known GLP-1 receptor agonist class effects.

›How does STEP-5 weight loss compare to bariatric surgery?

The 36.1% of STEP-5 participants who achieved ≥20% weight loss approach outcomes seen with some bariatric procedures (adjustable gastric banding typically produces 20-25% loss). Roux-en-Y gastric bypass produces greater average loss (30-35%), but pharmacotherapy avoids surgical risks.

›Did STEP-5 include patients with type 2 diabetes?

STEP-5 excluded patients with type 2 diabetes. The diabetes-specific durability question was addressed separately by STEP-2. STEP-5 enrolled adults with BMI ≥30, or ≥27 with at least one weight-related comorbidity other than diabetes.

›What was the dropout rate in STEP-5 over two years?

Approximately 13.2% of semaglutide-treated participants discontinued the trial drug, with 5.9% discontinuing due to adverse events. These rates are comparable to other long-term obesity pharmacotherapy trials and lower than many 104-week behavioral intervention studies.

›Does the STEP-5 weight-loss plateau mean the drug stopped working?

No. The plateau reflects the body reaching a new energy balance at a lower weight. Semaglutide continues to suppress appetite and reduce energy intake; the plateau occurs because metabolic adaptation (reduced resting energy expenditure at lower body mass) catches up to the reduced caloric intake.

›What did the SELECT trial add to STEP-5 findings?

SELECT (N=17,604) demonstrated that semaglutide 2.4 mg reduces major cardiovascular events by 20% over ~40 months, providing a hard-endpoint rationale for long-term use that goes beyond weight maintenance alone.

References

1. Garvey WT, Batterham RL, Bhatt DL, et al. Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial. Nat Med. 2022;28(10):2083-2091. PubMed

2. 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

3. 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

4. Wegovy (semaglutide) prescribing information. Novo Nordisk. Revised 2023. FDA Label

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