📚 Part of the GLP-1 Receptor Agonists Trial Guide — every landmark trial in one place.
Series: Landmark Trials in Endocrinology & Metabolism | Study #11
Category: GLP-1 Receptor Agonists · Obesity & Weight Management | Design: Multicentre, double-blind, placebo-controlled RCT | n: 1,961 | Follow-up: 68 weeks
📋 Summary
Authors: Wilding JPH et al., for the STEP 1 Study Group
Journal: N Engl J Med 2021;384:989–1002 | DOI: 10.1056/NEJMoa2032183
STEP 1 evaluated once-weekly subcutaneous semaglutide 2.4 mg — a dose substantially higher than the 1.0 mg dose approved for type 2 diabetes in the SUSTAIN programme — as an adjunct to lifestyle intervention in 1,961 adults with a BMI of 30 or more, or a BMI of 27 or more with at least one weight-related comorbidity, who did not have type 2 diabetes. Patients were randomly assigned in a 2:1 ratio to semaglutide 2.4 mg once weekly or placebo, both in conjunction with counselling on diet and physical activity, for 68 weeks. The co-primary endpoints were the percentage change in body weight from baseline and the proportion of participants achieving a weight reduction of 5% or more. At week 68, participants in the semaglutide group had lost a mean of 14.9% of body weight, compared with 2.4% in the placebo group (a difference of −12.4 percentage points; 95% CI −13.4 to −11.5; p<0.001). Weight reduction of 5% or more was achieved by 86.4% of the semaglutide group versus 31.5% of the placebo group, 10% or more by 69.1% versus 12.0%, 15% or more by 50.5% versus 4.9%, and 20% or more by 32.0% versus 1.7%. Waist circumference decreased by 13.54 cm in the semaglutide group versus 4.13 cm in the placebo group. Improvements were also observed in HbA1c, fasting plasma glucose, blood pressure, lipids, and markers of inflammation. Nausea, vomiting, and diarrhoea were the most common adverse events with semaglutide and led to treatment discontinuation in 4.5% of participants.
📊 Key Findings
| Outcome | Semaglutide 2.4 mg | Placebo | Effect Size |
|---|---|---|---|
| Mean % body weight change | −14.9% | −2.4% | Difference −12.4% (−13.4 to −11.5) · p<0.001 |
| ≥5% weight loss | 86.4% | 31.5% | p<0.001 |
| ≥10% weight loss | 69.1% | 12.0% | p<0.001 |
| ≥15% weight loss | 50.5% | 4.9% | p<0.001 |
| ≥20% weight loss | 32.0% | 1.7% | p<0.001 |
| Waist circumference change | −13.54 cm | −4.13 cm | Difference −9.4 cm · p<0.001 |
| HbA1c change | −0.37% | +0.12% | Difference −0.49% |
| GI adverse events leading to discontinuation | 4.5% | 0.8% | Predominant tolerability issue |
STEP 1 — Semaglutide 2.4 mg for weight loss
Phase 3 RCT · obesity without diabetes · 68 weeks
A 14.9% mean weight loss reset the ceiling for obesity pharmacotherapy, with a third of patients losing over 20%. The benefit requires ongoing treatment; gastrointestinal effects are the main tolerability issue.
💬 Expert Commentary
STEP 1 represented a genuine step change in the pharmacotherapy of obesity. Prior to this trial, the maximum weight loss achievable with approved pharmacological agents was approximately 5–10% with orlistat or phentermine-topiramate. A mean weight reduction of 14.9% in the semaglutide group, with a third of participants losing 20% or more, was unprecedented for a non-surgical intervention in a drug trial and placed semaglutide 2.4 mg in a different efficacy category from all previously available pharmacotherapy. The 68-week duration, while longer than most obesity drug trials, does not capture the long-term maintenance question; the STEP 4 trial subsequently demonstrated that weight regain occurs on discontinuation, confirming that the intervention requires ongoing administration for weight maintenance, as is the case with most chronic medications for chronic diseases.
The cardiometabolic secondary endpoint improvements, including reductions in HbA1c, blood pressure, waist circumference, and inflammation markers, are consistent with the known consequences of sustained weight loss but cannot be attributed exclusively to weight loss given the direct receptor-mediated effects of semaglutide on metabolism and appetite regulation. The question of whether the weight loss from semaglutide translates into hard cardiovascular endpoints in non-diabetic populations was left open by STEP 1 and was subsequently addressed by the SELECT trial (Study #13), which enrolled a population with established cardiovascular disease and demonstrated a 20% reduction in MACE. The mechanistic and clinical links between STEP 1 and SELECT are direct: SELECT enrolled participants who had achieved or could be expected to achieve the magnitude of weight loss demonstrated in STEP 1, and the cardiovascular benefit observed in SELECT reflects, at least in part, the consequences of that weight reduction.
Limitations: The trial duration of 68 weeks does not establish long-term weight loss maintenance (see STEP 4 for discontinuation data). Gastrointestinal adverse events are common and lead to discontinuation in a meaningful proportion of patients. The trial enrolled patients without type 2 diabetes; STEP 2 addressed the diabetic obesity population separately. The study was industry-sponsored by Novo Nordisk.
🔑 BOTTOM LINE
STEP 1 demonstrated that once-weekly semaglutide 2.4 mg produces unprecedented mean weight loss of 14.9% in adults with obesity without diabetes, with one third of participants losing more than 20% of body weight, fundamentally repositioning pharmacological obesity treatment as a genuinely impactful intervention rather than an adjunct with modest effect size.
⭐ Clinical Impact Rating: ●●●●● Practice-defining