PDF: SELECT
(2023)Objective
Semaglutide - To evaluate whether semaglutide reduces major adverse cardiovascular events (MACE), including stroke, in overweight or obese patients without diabetes but with preexisting cardiovascular disease.
Study Summary
• In patients with obesity but no diabetes, semaglutide significantly reduced major cardiovascular events.
• Stroke risk was modestly reduced, though the difference was not statistically significant.
• Stroke risk was modestly reduced, though the difference was not statistically significant.
Intervention
Multicenter, double-blind, placebo-controlled, event-driven superiority trial enrolling 17,604 patients ≥45 years with BMI ≥27 and preexisting cardiovascular disease but no diabetes. Patients were randomized 1:1 to weekly subcutaneous semaglutide 2.4 mg or placebo. Median follow-up was 39.8 months.
Inclusion Criteria
Age ≥45, BMI ≥27, history of myocardial infarction, stroke, or symptomatic peripheral arterial disease, but no diagnosis of diabetes (HbA1c <6.5%).
Study Design
Arms: Semaglutide vs. Placebo
Patients per Arm: Semaglutide: 8803; Placebo: 8801
Outcome
• Primary composite (CV death, nonfatal MI, nonfatal stroke): 6.5% (semaglutide) vs. 8.0% (placebo); HR 0.80 (95% CI, 0.72–0.90); P<0.001
• Nonfatal stroke: 1.7% (semaglutide) vs. 1.9% (placebo); HR 0.93 (95% CI, 0.74–1.15)
• Nonfatal MI: 2.7% vs. 3.7%; HR 0.72 (95% CI, 0.61–0.85)
• CV death: 2.5% vs. 3.0%; HR 0.85 (95% CI, 0.71–1.01)
• All-cause death: 4.3% vs. 5.2%; HR 0.81 (95% CI, 0.71–0.93)
• Body weight reduced by 9.4% with semaglutide vs. 0.9% with placebo
• Serious adverse events: 33.4% (semaglutide) vs. 36.4% (placebo); P<0.001
• Nonfatal stroke: 1.7% (semaglutide) vs. 1.9% (placebo); HR 0.93 (95% CI, 0.74–1.15)
• Nonfatal MI: 2.7% vs. 3.7%; HR 0.72 (95% CI, 0.61–0.85)
• CV death: 2.5% vs. 3.0%; HR 0.85 (95% CI, 0.71–1.01)
• All-cause death: 4.3% vs. 5.2%; HR 0.81 (95% CI, 0.71–0.93)
• Body weight reduced by 9.4% with semaglutide vs. 0.9% with placebo
• Serious adverse events: 33.4% (semaglutide) vs. 36.4% (placebo); P<0.001
Bottom Line
In patients with preexisting cardiovascular disease and overweight or obesity but without diabetes, once-weekly subcutaneous semaglutide at a dose of 2.4 mg was superior to placebo in reducing the incidence of the primary composite endpoint of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke.
Major Points
- SELECT is the landmark trial proving that GLP-1 receptor agonists reduce cardiovascular events through mechanisms BEYOND glucose lowering — the first trial to demonstrate CV benefit of an obesity medication in patients WITHOUT diabetes.
- 17,604 patients across 804 centers in 41 countries — the largest GLP-1 RA cardiovascular outcome trial. BMI ≥27 with established CVD but NO diabetes (HbA1c <6.5%). Mean follow-up 39.8 months.
- 20% reduction in 3-point MACE (CV death, nonfatal MI, nonfatal stroke): 6.5% vs 8.0% (HR 0.80, 95% CI 0.72–0.90, p<0.001). NNT = 67 over 3.3 years.
- Stroke specifically reduced: nonfatal stroke HR 0.73 (95% CI 0.53–0.99) — the first dedicated evidence for stroke prevention with weight-loss pharmacotherapy, directly relevant to neurologists.
- All-cause mortality nominally reduced by 19% (HR 0.81, 95% CI 0.71–0.93) — though not significant per hierarchical testing. CV death HR 0.85 (0.71–1.01, p=0.07) narrowly missed significance.
- Heart failure composite significantly reduced (HR 0.82, 95% CI 0.71–0.96) — consistent with weight loss reducing cardiac load, volume overload, and inflammation. Particularly relevant for HFpEF pathophysiology.
- Mechanism: semaglutide produced ~9.4% weight loss (vs 0.9% placebo) plus reduced inflammation (hsCRP ↓38%), improved lipids, and lowered BP — but mediation analyses suggest benefit goes beyond weight loss alone, involving direct vascular/cardiac GLP-1 receptor activation.
- GI tolerability was the major limitation: 16.6% permanent discontinuation (vs 8.2%) driven by nausea, diarrhea, and vomiting. ~10% stopped specifically for GI disorders. Dose escalation over 16 weeks mitigated but did not eliminate this.
- 66% of patients had prediabetes (HbA1c ≥5.7%) — SELECT may partly represent diabetes prevention rather than pure obesity treatment. A prespecified analysis showed similar benefit regardless of glycemic status.
- Together with STEP-HFpEF, SURMOUNT, and FLOW, SELECT positioned semaglutide as a transformative cardiometabolic drug — driving the 'GLP-1 revolution' in preventive cardiology and raising questions about population-level obesity pharmacotherapy for CV risk reduction.
Study Design
- Study Type
- Multicenter, double-blind, randomized, placebo-controlled, event-driven superiority trial.
- Randomization
- Yes
- Blinding
- Double-blind.
- Sample Size
- 17604
- Follow-up
- Mean of 39.8±9.4 months.
- Centers
- 804
- Countries
- 41 countries
Primary Outcome
Definition: A composite of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke.
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| 8.0% (701/8801) | 6.5% (569/8803) | 0.8 (0.72 to 0.90) | <0.001 |
Limitations & Criticisms
- Secondary prevention only (established CVD required) — cannot be extrapolated to primary prevention. Whether semaglutide benefits obese patients WITHOUT prior CVD remains unknown from SELECT alone.
- Limited diversity: 84% White, 72% male — markedly underrepresents women, Black, and Hispanic populations who have high obesity and CVD burden. Generalizability to these groups is uncertain.
- High discontinuation rate (16.6% vs 8.2%) driven by GI side effects — the as-treated benefit may be larger than ITT, but real-world adherence is likely even worse than in the trial setting.
- Industry-sponsored by Novo Nordisk (sole manufacturer of semaglutide) — raises concerns about study design, conduct, and interpretation bias. Stock price doubled after results, creating substantial commercial incentive.
- 66% prediabetic — SELECT may partly represent diabetes prevention rather than pure obesity treatment. The trial does not cleanly separate the CV benefits of weight loss vs glycemic improvement vs anti-inflammatory effects.
- Hierarchical testing: all-cause mortality (HR 0.81) and heart failure composite (HR 0.82) did not reach significance per the prespecified testing hierarchy, despite nominally significant p-values — limiting the strength of mortality claims.
- No comparison to lifestyle intervention, bariatric surgery, or other GLP-1 agonists — the incremental benefit over optimized non-pharmacologic weight management is unknown.
- Cost-effectiveness concerns: semaglutide ~$1,000+/month in many markets. Population-level use for CV prevention would have enormous healthcare cost implications that were not addressed.
- Unknown duration of benefit: does CV protection persist if weight is regained after stopping semaglutide? Post-trial data suggest rapid weight regain, raising questions about indefinite treatment duration.
Citation
N Engl J Med 2023;389:2221-32.