SELECT Trial: Semaglutide and Heart Attack Risk

Research-informed explainer — last updated 2026-04-11

The SELECT trial, published in the New England Journal of Medicine in 2023, showed that semaglutide 2.4 mg reduced the risk of heart attack, stroke, and cardiovascular death by 20% compared to placebo in people with obesity and established heart disease — and none of them had diabetes. It was the first trial to prove that a weight-loss medication could reduce serious cardiovascular events in people without diabetes, and it directly changed how the FDA labels Wegovy.

This explainer draws on peer-reviewed research from three endocrinologists in the Convene directory whose published work spans the SELECT trial itself, the cardiovascular biology of weight loss, and the clinical guidelines that govern how GLP-1 receptor agonists are prescribed.

What SELECT was designed to test

Before SELECT, there was a reasonable assumption that semaglutide's cardiovascular benefits (already demonstrated in people with type 2 diabetes) might partly reflect better blood sugar control. Lower glucose, less glycation of blood vessel walls, less oxidative stress — that is a plausible chain.

SELECT was designed to isolate the question. The researchers enrolled 17,604 adults with a body mass index of 27 or higher and pre-existing cardiovascular disease — people who had already had a heart attack, stroke, or peripheral artery disease — but who did not have diabetes. If semaglutide still reduced cardiovascular events in this group, blood sugar reduction could not be the explanation. The drug would have to be doing something else.

Participants were randomized to weekly subcutaneous semaglutide 2.4 mg or placebo. The trial ran for a median of 39.8 months — roughly three and a half years. The primary endpoint was a composite of cardiovascular death, non-fatal myocardial infarction (heart attack), or non-fatal stroke, a measure researchers call MACE (major adverse cardiovascular events) [1].

The key numbers

The results were unambiguous. Semaglutide reduced the primary endpoint by 20% compared to placebo: hazard ratio 0.80 (96.2% confidence interval, 0.72 to 0.90; p<0.001) [1].

In concrete terms, the primary endpoint occurred in 6.5% of participants in the semaglutide group versus 8.0% in the placebo group over the trial period. That gap, 1.5 percentage points in absolute terms, reflects a meaningful reduction in events across a large, high-risk population. Each component of MACE — cardiovascular death, heart attack, stroke — moved in the same direction.

The average weight loss in the semaglutide group was approximately 9.4% of body weight at two years. The placebo group lost about 0.9%. The question the trial could not fully answer — because it was not designed to — is how much of the cardiovascular benefit came from the weight loss itself versus direct effects of the drug on the cardiovascular system independent of weight.

How SELECT compares to earlier semaglutide trials

SELECT was not the first trial to show semaglutide reducing cardiovascular events. The SUSTAIN-6 trial, published in the New England Journal of Medicine in 2016, enrolled 3,297 people with type 2 diabetes at high cardiovascular risk and found a 26% reduction in MACE (hazard ratio 0.74) with subcutaneous semaglutide compared to placebo [2]. PIONEER-6, published in 2019, tested oral semaglutide in 3,183 patients with type 2 diabetes and cardiovascular risk and found a hazard ratio of 0.79 — directionally consistent, though that trial was an event-driven safety study rather than a superiority trial [3].

The pattern across SUSTAIN-6, PIONEER-6, and SELECT is strikingly consistent: hazard ratios of 0.74, 0.79, and 0.80, all pointing in the same direction. What SELECT added was the demonstration that the benefit does not depend on diabetes being present. The cardiovascular protection appears to be a property of semaglutide itself, not a downstream consequence of glucose lowering.

What might explain the benefit — beyond weight loss

Obesity drives cardiovascular disease through multiple pathways simultaneously. Research on intensive weight loss interventions has shown that even modest weight reductions of 5 to 10% produce measurable improvements in blood pressure, triglycerides, HDL cholesterol, insulin resistance, and markers of systemic inflammation [4]. Larger losses compound those benefits further [5]. The roughly 9% weight loss in the semaglutide arm of SELECT is consistent with the range where cardiovascular risk factors improve meaningfully.

But endocrinologists and cardiologists reviewing SELECT have raised the possibility that semaglutide does more than reduce weight. GLP-1 receptors are present not only in the pancreas but in the heart, blood vessels, and the brain. Animal and human studies suggest that GLP-1 receptor agonism may reduce inflammation in atherosclerotic plaques, lower blood pressure through mechanisms independent of weight, improve endothelial function, and slow the progression of plaque — effects that could stabilize vulnerable lesions and reduce the likelihood that a plaque ruptures and causes a heart attack.

The fact that the cardiovascular benefit in SELECT appeared relatively early in the trial — before substantial weight loss had accumulated — has been cited by some researchers as suggestive evidence for weight-loss-independent effects. This remains an active area of investigation, and the SELECT trial was not designed to disentangle these mechanisms.

What changed after SELECT

In March 2024, the FDA approved a new indication for Wegovy (semaglutide 2.4 mg) specifically to reduce the risk of serious cardiovascular events in adults with obesity or overweight and established cardiovascular disease. This made Wegovy the first anti-obesity medication in history to carry a cardiovascular risk reduction label.

That label change has real-world implications. Insurers that had previously declined to cover Wegovy for weight loss have faced pressure to cover it when prescribed for cardiovascular risk reduction — a different indication with a different evidence base. Cardiology and endocrinology professional societies have updated their guidance to account for SELECT. The AACE comprehensive diabetes management algorithm had already incorporated cardiovascular outcome data from GLP-1 trials as a decision-making factor in selecting diabetes medications [6][7]. SELECT extended that framework beyond diabetes into the broader population of people with obesity and heart disease.

Who does this apply to — and who it does not

The SELECT trial enrolled a specific population: adults with BMI of 27 or higher, pre-existing cardiovascular disease (prior heart attack, stroke, or peripheral artery disease), and no diabetes at baseline. The results apply most directly to people who match that profile.

Important caveats:

Established CVD is required. SELECT was a secondary prevention trial — all participants had already had a cardiovascular event or had documented cardiovascular disease. The trial does not provide evidence for primary prevention (reducing cardiovascular events in people who have not yet had one). Whether semaglutide reduces MACE in people with obesity and cardiovascular risk factors but no prior events is a separate question that SELECT does not answer.

No diabetes at baseline. People with type 2 diabetes already have GLP-1 receptor agonists available under diabetes indications. SELECT specifically addressed the gap population: people with obesity, heart disease, and no diabetes.

The trial included mostly older adults with serious prior cardiac events. The mean age was about 62, and the population was at genuinely high cardiovascular risk. How well the results generalize to younger adults or to people with less severe cardiovascular history is uncertain.

Side effects are real. In SELECT, gastrointestinal adverse events — nausea, vomiting, diarrhea — were more common with semaglutide than placebo and were the most frequent reason for discontinuation. The drug requires dose titration over several months to minimize these effects. Pancreatitis and gallbladder disease also occurred at somewhat higher rates in the semaglutide group.

The weight-loss-independent CV benefit hypothesis

One of the most scientifically significant questions SELECT raises is whether the cardiovascular benefit requires meaningful weight loss, or whether the drug has direct cardioprotective effects that would occur even without substantial weight reduction.

Several observations fuel this debate. GLP-1 receptors are expressed in cardiomyocytes and vascular smooth muscle cells. Studies have found that GLP-1 receptor agonism reduces inflammatory cytokines relevant to atherosclerosis, improves coronary flow reserve, and may reduce the lipid content of atherosclerotic plaques independently of systemic weight loss. The early separation of cardiovascular event curves in SELECT is consistent with an effect that does not wait for the full weight-loss trajectory to unfold.

At the same time, the mechanistic evidence does not yet permit a clear conclusion. Weight loss itself has robust effects on every major cardiovascular risk factor, and the 9% average weight loss in SELECT is not trivial. Most likely, both mechanisms contribute. The relative magnitude of each is a question current research has not resolved.

Questions to ask your cardiologist or endocrinologist

• Do I have established cardiovascular disease? Have I had a prior heart attack, stroke, or been diagnosed with peripheral artery disease?
• Is my BMI above 27? Do I meet the SELECT profile for the cardiovascular indication?
• Do I have type 2 diabetes, or is my glucose in the normal range? That changes which indication and which dosing applies.
• How does Wegovy for cardiovascular risk reduction compare to other risk-reduction strategies I am already on, such as statins, blood pressure medications, or aspirin?
• What gastrointestinal side effects should I expect, and how long does the titration period take?
• If I cannot tolerate the medication, what are the alternatives?
• Will my insurer cover Wegovy under the cardiovascular indication, and what documentation does my doctor need to submit?

The bottom line

The SELECT trial answered a question that had never been asked in a large randomized trial: does a weight-loss medication reduce serious cardiovascular events in people without diabetes? The answer was yes — a 20% reduction in heart attack, stroke, and cardiovascular death over roughly three and a half years, in 17,604 people with obesity and established cardiovascular disease. That finding is consistent with earlier data from semaglutide trials in people with type 2 diabetes (SUSTAIN-6 and PIONEER-6), and it led directly to a new FDA indication and a shift in how endocrinologists and cardiologists think about prescribing Wegovy.

SELECT does not apply to everyone with obesity. It applies most directly to people who have already had a cardiovascular event, carry a BMI of 27 or higher, and do not have diabetes. If you fit that profile, the trial's evidence is relevant to your care. Bring the questions above to your doctor — the conversation has moved well beyond weight loss.