STEP-2 Results in Detail: Numbers, Subgroups, and Time Course

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At a glance

| Parameter | Detail | |-----------|--------| | N | 1,210 randomized | | Intervention | Semaglutide 2.4 mg subcutaneous once weekly | | Active comparator | Semaglutide 1.0 mg once weekly | | Placebo | Matched injection + lifestyle intervention | | Duration | 68 weeks (16-week dose escalation + 52 weeks maintenance) | | Primary endpoint | Percentage change in body weight from baseline to week 68 | | Key result | -9.6% (sema 2.4 mg) vs -7.0% (sema 1.0 mg) vs -3.4% (placebo) | | Population | Adults with BMI ≥27, T2D, HbA1c 7-10% |

Why STEP-2 Matters Beyond the Abstract

The STEP-1 trial demonstrated that semaglutide 2.4 mg could produce nearly 15% weight loss in adults without diabetes. But patients with type 2 diabetes typically lose less weight with any intervention due to insulin resistance, concurrent medications that promote weight gain, and compensatory metabolic adaptations. STEP-2 was designed specifically to quantify this attenuation and determine whether the 2.4 mg dose still delivered clinically relevant results in this harder-to-treat population.

The trial also included a semaglutide 1.0 mg arm (the dose already approved for glycemic control under the brand Ozempic), allowing direct comparison between the diabetes-approved dose and the higher obesity-indication dose.

Primary Endpoint: Weight Change at Week 68

The estimated treatment difference for semaglutide 2.4 mg versus placebo was -6.2 percentage points (95% CI: -7.3 to -5.2; p <0.0001). In absolute terms:

| Arm | Mean % weight change | 95% CI | Absolute loss (kg) | |-----|---------------------|--------|---------------------| | Semaglutide 2.4 mg (n=404) | -9.64% | -10.58 to -8.70 | ~9.7 kg | | Semaglutide 1.0 mg (n=403) | -7.01% | -7.94 to -6.08 | ~7.0 kg | | Placebo (n=403) | -3.42% | -4.35 to -2.49 | ~3.4 kg |

These results used the treatment policy estimand, meaning all participants were included regardless of treatment discontinuation or rescue medication use. Under the trial product estimand (on-treatment analysis), losses were slightly larger: -10.6% for sema 2.4 mg and -8.1% for sema 1.0 mg.

Response Distribution: Who Lost How Much

The categorical responder analysis revealed meaningful separation between arms:

| Threshold | Sema 2.4 mg | Sema 1.0 mg | Placebo | |-----------|-------------|-------------|---------| | ≥5% weight loss | 68.8% | 57.1% | 28.5% | | ≥10% weight loss | 45.6% | 28.7% | 8.2% | | ≥15% weight loss | 25.8% | 13.4% | 3.2% | | ≥20% weight loss | 11.1% | 6.0% | 1.5% |

These numbers tell a story the mean obscures. About one in four patients on the high dose achieved ≥15% loss, a threshold associated with remission of obesity-related comorbidities. Conversely, roughly 31% on the 2.4 mg dose did not reach the 5% threshold commonly considered clinically significant. This heterogeneity mirrors real-world practice: GLP-1 receptor agonists produce variable responses even within a tightly selected trial population.

Time-Course Pattern: When Does Weight Loss Plateau?

Weight loss in the semaglutide 2.4 mg arm followed a characteristic trajectory:

  • Weeks 0-16 (dose escalation): Rapid initial loss during the 0.25 mg to 2.4 mg titration period. By week 16, participants had already lost approximately 5-6% of body weight.
  • Weeks 16-40: Continued loss at a decelerating rate. The steepest portion of the curve occurred between weeks 8 and 28.
  • Weeks 40-68: Near-plateau in the group mean, with weight stabilizing around weeks 56-60 in most participants.

The placebo arm showed early modest loss (likely from the lifestyle intervention component) that flattened by week 20 and showed slight regain trends after week 52. The 1.0 mg arm tracked between the two, plateauing earlier (around week 44) at a lower nadir than the 2.4 mg group.

This time course has direct clinical implications. Patients who see no meaningful response by week 20-24 at full dose are unlikely to become late responders, a pattern consistent across the STEP program and relevant to insurance coverage continuation criteria.

Secondary Endpoints: Beyond the Scale

Glycemic Control

HbA1c reductions were substantial and dose-dependent:

| Arm | HbA1c change from baseline | Patients achieving HbA1c <7% | |-----|---------------------------|-------------------------------| | Sema 2.4 mg | -1.6 percentage points | 78.6% | | Sema 1.0 mg | -1.5 percentage points | 72.3% | | Placebo | -0.4 percentage points | 26.7% |

Baseline mean HbA1c was approximately 8.1% across arms. The glycemic benefit of sema 2.4 mg compared to sema 1.0 mg was modest (0.1 percentage point difference), suggesting that most of the glucose-lowering capacity is captured at the 1.0 mg dose, while the additional weight loss at 2.4 mg provides incremental but smaller glycemic benefit.

Cardiometabolic Markers

Semaglutide 2.4 mg produced improvements across several secondary cardiometabolic endpoints versus placebo:

  • Waist circumference: -9.4 cm vs -4.5 cm (placebo)
  • Systolic blood pressure: -3.9 mmHg vs -0.5 mmHg
  • C-reactive protein: Significant reductions (exact values varied by analysis)
  • Fasting lipids: Modest improvements in triglycerides and HDL-C

These changes align with the magnitude expected from ~10% weight loss and are consistent with cardiovascular benefit signals seen in the SELECT trial for semaglutide in patients with established cardiovascular disease.

Physical Functioning

Patient-reported outcomes using the SF-36 physical functioning domain showed statistically significant improvement with sema 2.4 mg versus placebo. The IWQOL-Lite-CT (Impact of Weight on Quality of Life) physical function score also favored the 2.4 mg group.

Subgroup Analyses

Pre-specified subgroup analyses examined consistency of the primary endpoint across:

  • Baseline BMI (<35 vs ≥35): Effect was consistent. Patients with higher baseline BMI lost more absolute weight but similar percentages.
  • Baseline HbA1c (<8.5% vs ≥8.5%): Those with higher baseline HbA1c showed slightly attenuated weight loss, possibly reflecting greater insulin resistance or use of weight-promoting diabetes medications.
  • Number of oral antidiabetic drugs (1 vs 2-3): No meaningful interaction.
  • Sex: Women tended toward slightly greater percentage weight loss, consistent with other GLP-1 RA trials.
  • Age (<65 vs ≥65): No significant interaction, though the older subgroup had smaller absolute numbers.
  • Race/ethnicity: The trial enrolled a predominantly White population (61%), with 12% Black participants. Subgroup point estimates were consistent though confidence intervals were wide for smaller groups.

Safety Results Relevant to Efficacy Interpretation

Gastrointestinal adverse events occurred in 63.5% of the sema 2.4 mg group versus 34.3% on placebo. Nausea (34.5%), diarrhea (21.2%), and vomiting (15.4%) were the most common. Most events were mild to moderate and occurred primarily during dose escalation.

Treatment discontinuation due to adverse events was 5.9% for sema 2.4 mg, 4.2% for sema 1.0 mg, and 3.5% for placebo. This relatively low discontinuation rate suggests the efficacy estimates were not heavily biased by differential dropout of intolerant patients.

Gallbladder-related disorders occurred more frequently with semaglutide (2.6% for 2.4 mg vs 1.2% placebo), consistent with the known risk of gallstone formation during rapid weight loss.

Comparison to STEP-1 (Non-Diabetic Population)

The attenuation of weight loss in T2D versus non-T2D populations is clearly quantified by comparing STEP-2 to STEP-1:

| Metric | STEP-1 (no T2D) | STEP-2 (T2D) | Difference | |--------|-----------------|--------------|------------| | Mean % weight loss (sema 2.4 mg) | -14.9% | -9.6% | ~5.3 pp less | | ≥10% responders | 69.1% | 45.6% | ~23.5 pp less | | ≥15% responders | 50.5% | 25.8% | ~24.7 pp less |

This ~35% relative attenuation in the T2D population aligns with historical patterns for anti-obesity medications and is attributed to insulin resistance impairing lipolysis, background medications that promote weight gain (sulfonylureas, insulin), and metabolic adaptation in the setting of chronic hyperinsulinemia.

Limitations the Authors Acknowledged

The STEP-2 investigators noted several important limitations:

  1. 68-week duration does not establish long-term durability. The STEP-4 extension and real-world data suggest weight regain after discontinuation.
  2. Excluded populations: Patients on insulin were excluded, limiting generalizability to more advanced T2D.
  3. Lifestyle intervention in all arms means the placebo response (3.4%) reflects active behavioral support, not true natural history.
  4. Single primary timepoint at 68 weeks does not capture whether the 2.4 mg group had reached true plateau or might continue losing.
  5. Predominantly White population limits ethnic/racial generalizability.

Clinical Translation

For prescribers considering semaglutide 2.4 mg (Wegovy) in patients with T2D, STEP-2 provides realistic expectations: approximately 10% mean weight loss, with about 46% of patients achieving ≥10% and one-quarter reaching ≥15%. These numbers should inform shared decision-making conversations. The FDA label for Wegovy includes STEP-2 data in its clinical studies section, supporting use in this population.

The 2.4 mg dose offers approximately 2.6 percentage points of additional weight loss over the 1.0 mg dose already available as Ozempic, with similar safety profiles. Whether this increment justifies the higher cost and separate prescription depends on individual patient goals and payer coverage decisions.

Frequently asked questions

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References

  1. Davies M, Færch L, Jeppesen OK, et al. Semaglutide 2.4 mg once a week in adults with overweight or obesity, and type 2 diabetes (STEP 2): a randomised, double-blind, double-dummy, placebo-controlled, phase 3 trial. Lancet. 2021;397(10278):971-984. https://pubmed.ncbi.nlm.nih.gov/33667417/
  2. FDA. Wegovy (semaglutide) injection prescribing information. 2021. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/215256s000lbl.pdf
  3. Wilding JPH, Batterham RL, Calanna S, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. https://pubmed.ncbi.nlm.nih.gov/33567185/
  4. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389(24):2221-2232. https://pubmed.ncbi.nlm.nih.gov/37952131/
  5. Rubino DM, Greenway FL, Khalid U, et al. Effect of weekly subcutaneous semaglutide vs daily liraglutide on body weight in adults with overweight or obesity without diabetes (STEP 8). JAMA. 2022;327(2):138-150. https://pubmed.ncbi.nlm.nih.gov/35441470/