GLP-1 Cardiovascular Outcomes Trials: SELECT, FLOW, and What Came After
SELECT: 20% MACE reduction in non-diabetic obesity (HR 0.80). FLOW: 24% composite kidney endpoint reduction, stopped early for overwhelming benefit. SURPASS-CVOT: 13% MACE reduction vs. an active GLP-1 control. A comprehensive CVOTs review.
The GLP-1 cardiovascular outcomes trial program has produced the most consequential evidence for these medications beyond weight loss. Here's a comprehensive review of the SELECT, FLOW, and subsequent CVOT data — what each trial was designed to test, what it found, and how the findings interact.
Why CVOTs Exist for These Medications
The FDA Guidance for Industry on cardiovascular outcomes for type 2 diabetes drugs (2008) established a requirement that new diabetes medications demonstrate cardiovascular safety through dedicated outcomes trials. GLP-1 agents for type 2 diabetes were among the first to complete these trials — and several showed cardiovascular benefit rather than just safety, shifting the regulatory and clinical conversation. The SELECT trial extended this to GLP-1 use in obesity without diabetes.
SELECT: The Landmark Trial
SELECT (Semaglutide and Cardiovascular Outcomes in Adults with Overweight or Obesity) enrolled 17,604 adults with BMI ≥27, established cardiovascular disease, and no diabetes. This was the first CVOT specifically in non-diabetic obesity. Follow-up: 34.4 months (median). Primary endpoint: first occurrence of MACE (cardiovascular death, non-fatal MI, non-fatal stroke).
| SELECT Endpoint | Semaglutide 2.4mg | Placebo | HR (95% CI) |
|---|---|---|---|
| Primary MACE | 6.5% | 8.0% | 0.80 (0.72–0.90) |
| Cardiovascular death | 2.5% | 3.1% | 0.85 (0.71–1.01) |
| Non-fatal MI | 3.5% | 4.5% | 0.74 (0.63–0.87) |
| Non-fatal stroke | 1.7% | 2.0% | 0.89 (0.70–1.11) |
| Heart failure hospitalization | 1.8% | 2.2% | 0.82 (0.65–1.04) |
FLOW: The Kidney Trial
FLOW (Semaglutide in Subjects with T2D and Chronic Kidney Disease) enrolled 3,534 patients with type 2 diabetes and CKD. It was stopped early by the independent data monitoring committee in March 2024 due to overwhelming efficacy. Primary endpoint: composite of sustained ≥50% eGFR decline, ESKD, kidney death, or cardiovascular death.
Results: semaglutide reduced the primary composite endpoint by 24% (HR 0.76, 95% CI 0.66–0.88). The kidney-specific outcomes drove the benefit — a finding that suggests direct GLP-1 receptor effects on the kidney, not only cardiovascular mediation.
SELECT's cardiovascular benefit exceeds what models based purely on weight loss would predict. For a 14% body weight reduction, expected MACE reduction from weight loss alone is estimated at 5–8% — below the 20% observed. Direct vascular effects — GLP-1 receptor expression in endothelium and myocardium, anti-inflammatory effects on atherosclerotic plaque, improvement in biomarkers beyond weight-sensitive parameters — are proposed mechanisms under active investigation. FLOW's kidney data similarly suggests organ-specific receptor-mediated effects beyond weight loss.
SURPASS-CVOT: Tirzepatide in T2D
SURPASS-CVOT, comparing tirzepatide to dulaglutide in type 2 diabetes, completed enrollment in 2023. Primary results were presented in late 2025: tirzepatide reduced MACE by 13% versus an active GLP-1 comparator (dulaglutide) — demonstrating cardiovascular benefit even against an active GLP-1 control. A tirzepatide CVOT in non-diabetic obesity (analogous to SELECT for semaglutide) has been announced but not yet reported.
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Sources
- Lincoff AM, et al. "Semaglutide and Cardiovascular Outcomes in Obesity Without Diabetes (SELECT)." NEJM. 2023.
- Perkovic V, et al. "Semaglutide and Kidney Outcomes in Type 2 Diabetes (FLOW)." NEJM. 2024.
- Gerstein HC, et al. "Tirzepatide versus Dulaglutide in T2D: SURPASS-CVOT." NEJM. 2025.
- Kristensen SL, et al. "Cardiovascular, mortality, and kidney outcomes with GLP-1 receptor agonists in patients with type 2 diabetes: a systematic review and meta-analysis." Lancet Diabetes Endocrinol. 2019.