Semaglutide and Heart Health: The SELECT Trial, Explained
The first trial to show a weight-loss drug can cut heart attacks and strokes, what the numbers really say, and who they apply to.
For years, drugs that help people lose weight were viewed mainly as tools for managing the number on the scale. The SELECT trial changed that conversation. It was the first large study to test whether a weight-loss medication could actually prevent heart attacks and strokes, and its results led to a first-of-its-kind regulatory approval. Here is what the trial found, who it applies to, and what it does not yet answer.
What the SELECT trial tested
SELECT enrolled 17,604 adults, split almost evenly between semaglutide (8,803 people) and a placebo (8,801 people). Participants were 45 or older, had a body mass index of at least 27, and already had established cardiovascular disease, meaning a prior heart attack, a prior stroke, or symptomatic peripheral artery disease. Importantly, they did not have diabetes. Everyone received either once-weekly semaglutide 2.4 mg, sold as Wegovy, or a placebo injection, on top of their usual care.
This enrollment picture matters more than any single statistic, because it defines exactly who the findings speak to: higher-risk patients who are trying to prevent a second cardiac event, not the general public and not people simply seeking weight loss.
The headline result
The trial's main goal was to see whether semaglutide reduced a combined measure called MACE, or major adverse cardiovascular events. This composite counted cardiovascular death, non-fatal heart attack, or non-fatal stroke, whichever came first. Over a mean follow-up of roughly 40 months, one of these events occurred in 6.5% of people taking semaglutide compared with 8.0% on placebo.
That works out to a 20% relative reduction in risk (hazard ratio 0.80, 95% confidence interval 0.72 to 0.90, p<0.001). It was the first cardiovascular outcomes trial to show that a weight-loss drug can cut cardiac events. But the two ways of describing the same result feel very different, and both are true at once.
A 20% relative reduction and a 1.5 percentage-point absolute difference describe the very same result. Neither should be quoted without the other.
The 20% figure is the relative reduction. In absolute terms, the gap was about 1.5 percentage points, 6.5% versus 8.0%, spread across more than three years. A general-audience takeaway should hold both framings side by side rather than leaning on the more dramatic one.
Reading the fine print
When researchers looked underneath the headline, the picture became more nuanced. The benefit was carried by the combined MACE measure rather than by any single outcome on its own:
- Non-fatal heart attack was less common with semaglutide (2.7% vs 3.7%; hazard ratio 0.72, 95% CI 0.61 to 0.85), a statistically significant difference.
- All-cause mortality trended lower (4.3% vs 5.2%; hazard ratio 0.81, 95% CI 0.71 to 0.93).
- Cardiovascular death alone did not reach statistical significance (hazard ratio 0.85, 95% CI 0.71 to 1.01, an interval that crosses 1.0).
- The trial was not designed to prove a benefit on each individual outcome separately, so the composite is where the evidence is strongest.
Weight loss, meanwhile, was substantial and lasting. Body weight fell about 10.2% with semaglutide versus 1.5% with placebo, an 8.7 percentage-point difference that plateaued around week 65 and held through 208 weeks, roughly four years. By week 104, about 67.8% of semaglutide patients had lost at least 5% of their body weight and 44.2% had lost at least 10%, compared with 21.3% and 6.9% on placebo. For context, an earlier weight-management trial, STEP 1, produced a mean weight change of -14.9% versus -2.4% at 68 weeks.
Here is a genuine surprise. A prespecified analysis found the cardiovascular benefit was largely independent of how much weight a person lost. There was no clear link between the amount of weight shed by week 20 and later cardiac risk. That suggests much of the heart benefit is not explained by weight loss alone, and it points toward possible direct effects on the blood vessels or on inflammation. This remains inferential, though, and the exact mechanism of the cardiovascular benefit is not established.
Benefits and trade-offs
Semaglutide came with real side effects. Gastrointestinal problems, including nausea, vomiting, and diarrhea, were far more common than with placebo. Adverse events leading people to stop the study drug occurred in 16.6% of the semaglutide group versus 8.2% on placebo. At the same time, serious adverse events overall were slightly lower with semaglutide (33.4% vs 36.4%), an unexpected reassurance on overall safety.
Beyond SELECT, a separate trial called STEP-HFpEF studied 529 people with obesity-related heart failure with preserved ejection fraction. Semaglutide improved symptom and function scores on a standard questionnaire by an estimated 7.8 points more than placebo (16.6 vs 8.7) and reduced body weight by 13.3% versus 2.6% over 52 weeks. That study measured how people felt and functioned; it was not designed or powered to show reductions in hard outcomes like death or hospitalization, so it demonstrates symptomatic benefit rather than a mortality benefit.
What it means, and what it does not
On March 8, 2024, the FDA approved Wegovy to reduce the risk of cardiovascular death, heart attack, and stroke in adults with established cardiovascular disease and either obesity or overweight, citing the same 6.5% versus 8.0% result. It was the first weight-loss medication approved for cardiovascular event prevention. The approved use is specific: as an addition to standard care, for adults with established cardiovascular disease, a BMI of at least 27, and without type 1 or type 2 diabetes.
Several honest limits are worth keeping in view. The trial population was predominantly older (mean age about 62), male (around 72%), and White (around 84%), which limits how confidently the findings extend to women, younger adults, and other groups. The results do not automatically apply to people without prior cardiovascular disease, to those with diabetes, or to the general public seeking weight loss. And SELECT was funded and co-designed by the manufacturer, Novo Nordisk. That is standard for pivotal trials, but it is a relevant disclosure. The bottom line is meaningful but bounded: for a specific, higher-risk group, semaglutide reduced cardiac events, through a pathway that is still not fully understood.
- 01 SELECT primary trial: MACE 6.5% vs 8.0%, HR 0.80 (0.72-0.90); secondary endpoints and safety.
- 02 American College of Cardiology SELECT trial summary (and ClinicalTrials.gov NCT03574597), 2023 acc.org ↗Trial population: 17,604 adults 45+, BMI >=27, established cardiovascular disease, without diabetes.
- 03 FDA Press Announcement, 2024 fda.gov ↗March 8, 2024 approval of Wegovy to reduce risk of cardiovascular death, heart attack, and stroke.
- 04 Peer-reviewed review of the semaglutide cardiovascular indication (PMC12187477), 2025 pmc.ncbi.nlm.nih.gov ↗Exact wording of the approved cardiovascular indication (BMI >=27, without type 1 or type 2 diabetes); mechanism not specifically known.
- 05 Ryan DH et al., Nature Medicine (PMC11271387), 2024 pmc.ncbi.nlm.nih.gov ↗Long-term weight loss in SELECT: ~10.2% vs 1.5%, sustained through 208 weeks; week-104 responder rates.
- 06 Cardiovascular benefit largely independent of the amount of weight lost; no more than ~33% mediated by waist-circumference change.
- 07 STEP 1 weight-management trial: -14.9% vs -2.4% body weight at 68 weeks.
- 08 STEP-HFpEF: symptom score +7.8 points vs placebo (16.6 vs 8.7); weight -13.3% vs -2.6% at 52 weeks.
Wellness Wire Editorial
The Wellness Wire editorial team. Our explainers are researched from primary sources — clinical-trial reports and FDA labeling — and written for general education. They are not individually reviewed by a clinician and are not a substitute for medical advice.
