STEP, SELECT, and Real-World Weight Loss: What the Trials Actually Showed

STEP-1 — the foundational weight-loss trial

STEP-1 (Wilding et al., NEJM 2021) randomized 1,961 adults with BMI ≥30 (or ≥27 with comorbidity) to once-weekly subcutaneous semaglutide 2.4 mg or placebo for 68 weeks alongside lifestyle intervention.

• Mean weight change: -14.9% semaglutide vs -2.4% placebo
• ≥5% weight loss: 86.4% vs 31.5%
• ≥10% weight loss: 69.1% vs 12.0%
• ≥15% weight loss: 50.5% vs 4.9%

Most common adverse events: GI — nausea, diarrhea, constipation, vomiting — typically transient and dose-related.

STEP-3 and STEP-4 — context

• STEP-3: Semaglutide 2.4 mg + intensive behavioral therapy + low-cal diet vs placebo + same. Mean loss: -16.0% vs -5.7%.
• STEP-4: Weight maintenance after initial loss. Patients continuing semaglutide maintained additional loss; those switched to placebo regained weight.

SELECT — the cardiovascular outcomes trial

SELECT (Lincoff et al., NEJM 2023) randomized 17,604 adults aged ≥45 with established cardiovascular disease and BMI ≥27 to semaglutide 2.4 mg or placebo over a mean 39.8 months. Primary endpoint: MACE (composite of CV death, nonfatal MI, nonfatal stroke).

• Primary endpoint: 6.5% semaglutide vs 8.0% placebo — HR 0.80 (95% CI 0.72-0.90), p<0.001
• 20% relative risk reduction in major cardiovascular events
• CV death: 2.5% vs 3.0% (HR 0.85)

SELECT's results led to Wegovy's FDA-approved label expansion for cardiovascular risk reduction in adults with CV disease and overweight or obesity, regardless of diabetes status.

What the trials mean for compounded semaglutide

STEP-1 and SELECT used brand-name semaglutide produced by Novo Nordisk under cGMP. Compounded semaglutide is a state-licensed 503A or FDA-registered 503B preparation. Same molecule, but compounded preparations are not bioequivalent in the FDA-regulatory sense:

• Concentration may differ (brand: 2.4 mg/0.75 mL; compounded: varies)
• Excipients differ; absorption and tolerability may differ
• Compounding-pharmacy QC varies; potency consistency between batches depends on pharmacy

Patients on compounded semaglutide may experience outcomes similar to STEP-1 — and many do — but cannot rely on the trial data for direct outcome prediction.

Real-world outcome moderators

1. Adherence to titration — patients who don't reach maintenance dose plateau early
2. Concurrent lifestyle changes — diet, physical activity, sleep, behavior
3. Side-effect tolerability — patients who can't tolerate maintenance see smaller effects
4. Concurrent medications — some attenuate GLP-1 effects
5. Duration of treatment — STEP-1 was 68 weeks; 6-month outcomes are smaller

Frequently asked questions