SELECT Trial: A Plain-English Overview of What It Established

At a glance

• Full title: Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes (SELECT)
• N: 17,604
• Intervention: Subcutaneous semaglutide 2.4 mg once weekly
• Comparator: Matching placebo
• Duration: Median follow-up of 39.8 months (event-driven design)
• Primary endpoint: Time to first major adverse cardiovascular event (MACE), defined as cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke
• Key result: 20% relative risk reduction in MACE (HR 0.80; 95% CI 0.72 to 0.90; P <0.001)

The question SELECT set out to answer

Before SELECT, the medical world had a frustrating gap. GLP-1 receptor agonists like semaglutide had proven cardiovascular benefits in people with type 2 diabetes (the SUSTAIN-6 and PIONEER 6 trials showed this clearly). Weight-loss drugs, on the other hand, had a troubled regulatory history. The FDA had pulled multiple obesity medications for cardiovascular safety concerns over the decades. No weight-loss drug had ever demonstrated that it could prevent heart attacks and strokes.

SELECT asked a specific, high-stakes question: In people who are overweight or obese, who already have atherosclerotic cardiovascular disease, and who do not have diabetes, does semaglutide 2.4 mg reduce the rate of major cardiovascular events?

The "without diabetes" part matters. It removed the confounding glucose-lowering benefit of semaglutide. If cardiovascular protection showed up anyway, it would suggest the drug was doing something beyond blood-sugar control. Something related to weight loss, inflammation, or direct vascular effects.

Who was enrolled

The trial recruited participants aged 45 or older with a BMI of 27 kg/m² or higher. Every participant had to have confirmed atherosclerotic cardiovascular disease, meaning a prior heart attack, prior stroke, or symptomatic peripheral artery disease. Participants with type 1 or type 2 diabetes were excluded, as were those with an HbA1c of 6.5% or above at screening. People who had used GLP-1 receptor agonists in the preceding 90 days were also excluded.

The average participant was about 61.6 years old with a BMI around 33.3 kg/m². Roughly 72% were male. The population was heavily treated at baseline: around 90% were on statins, approximately 86% were on antiplatelet therapy, and about 75% used antihypertensives. This is important because it means semaglutide was tested on top of already-optimized standard care, not as a substitute for it.

About 70% of participants had a history of myocardial infarction. Nearly 24% had a prior stroke. The trial enrolled from over 800 sites across 41 countries.

What participants received

Participants were randomized 1:1 to receive either semaglutide or a visually identical placebo, injected subcutaneously once weekly. The dose was escalated over 16 weeks following a standard titration schedule: 0.25 mg for weeks 1 through 4 to 0.5 mg for weeks 5 through 8 to 1.0 mg for weeks 9 through 12 to 1.7 mg for weeks 13 through 16, and 2.4 mg from week 17 onward. This matches the Wegovy prescribing information dosing schedule.

Participants who could not tolerate the full 2.4 mg dose were allowed to step down to 1.7 mg. About 16.6% of the semaglutide group did not reach or maintain the 2.4 mg target dose, compared to 8.2% in the placebo group (largely because gastrointestinal side effects are more common on the active drug).

Both groups continued their usual cardiovascular medications throughout the trial. There were no mandated diet or exercise programs, though participants received general lifestyle counseling.

How the primary endpoint was measured

SELECT was an event-driven trial, meaning it did not end after a fixed number of months. It continued until a prespecified number of adjudicated MACE events (1,225) had occurred. An independent, blinded clinical-events committee reviewed every potential endpoint event. This approach is standard for cardiovascular outcome trials and gives the analysis more statistical power than a fixed-duration design.

The primary endpoint was a three-component MACE: cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke. Time-to-event analysis used a Cox proportional-hazards model, stratified by the qualifying cardiovascular condition (prior MI, prior stroke, or peripheral artery disease) and by region.

The trial used an intention-to-treat approach, meaning every randomized participant counted in the analysis regardless of whether they stayed on the medication. This is the most conservative analytic strategy because people who stop the drug (which happened more often in the semaglutide group due to side effects) still count toward the drug's result.

What SELECT found

Primary endpoint

Semaglutide reduced three-point MACE by 20% compared to placebo (HR 0.80; 95% CI 0.72 to 0.90; P <0.001). In absolute terms, a primary-endpoint event occurred in 6.5% of the semaglutide group versus 8.0% of the placebo group over the median 39.8-month follow-up.

The benefit was most clearly driven by reductions in nonfatal myocardial infarction (28% relative risk reduction). Cardiovascular death showed a 15% reduction that did not reach statistical significance on its own. Nonfatal stroke showed a non-significant 7% reduction.

Weight loss and metabolic effects

By week 104, participants on semaglutide lost an average of 9.4% of their body weight, compared to 0.9% in the placebo group. Waist circumference decreased by about 7.7 cm on semaglutide versus 1.3 cm on placebo. C-reactive protein (a marker of systemic inflammation) dropped by approximately 38% more on semaglutide than on placebo.

Systolic blood pressure decreased by roughly 3.4 mmHg more on semaglutide. HbA1c fell by about 0.3 percentage points more in the semaglutide group, and fewer semaglutide-treated participants developed new-onset type 2 diabetes during the trial (about 1.6% vs. 3.0%).

Subgroup consistency

The MACE benefit was broadly consistent across prespecified subgroups, including by sex, age, baseline BMI, race, qualifying cardiovascular condition, and baseline HbA1c. There was no clear signal that the benefit was limited to any particular patient subset. The benefit appeared similar in people with BMI 27 to <30 and those with BMI 30 or higher.

Safety and tolerability

Gastrointestinal adverse events were the most common reason for drug discontinuation. Nausea occurred in 17.1% of the semaglutide group versus 7.0% on placebo. Diarrhea occurred in 11.5% versus 7.6%. Vomiting occurred in 8.4% versus 2.6%. Most GI events were mild to moderate and occurred during the dose-escalation phase.

Permanent treatment discontinuation was higher in the semaglutide group: 16.6% versus 8.2% for placebo. This is a clinically meaningful dropout rate, though it mirrors rates seen in other semaglutide trials at the 2.4 mg dose.

Serious adverse events occurred at similar rates in both groups (33.4% semaglutide vs. 36.4% placebo). Pancreatitis was rare and occurred at similar frequency (0.2% in each group). Cholelithiasis (gallstones) was more common on semaglutide (2.8% vs. 2.3%). There were no significant differences in rates of thyroid cancer, though the trial was not powered or designed to detect rare thyroid malignancies.

Limitations the authors acknowledged

The trial was not designed to assess all-cause mortality as a primary endpoint and did not show a statistically significant reduction in all-cause death. The investigators noted that the trial's follow-up duration may have been insufficient to detect mortality differences.

Adherence was imperfect. As noted, 16.6% of the semaglutide group discontinued. The intention-to-treat analysis likely diluted the true treatment effect among people who stayed on the drug.

The trial enrolled participants with established cardiovascular disease. Results may not apply to people without pre-existing heart or vascular conditions (primary prevention). The American Heart Association's 2023 guidelines were updated following SELECT but noted this distinction.

SELECT excluded people with diabetes, which means the findings cannot be directly combined with SUSTAIN-6 results to estimate effects across both populations simultaneously.

Finally, the trial tested only the 2.4 mg dose of semaglutide. Whether lower doses (0.5 mg, 1.0 mg) provide proportional cardiovascular protection remains unknown.

What changed after SELECT

The FDA approved a new indication for Wegovy (semaglutide 2.4 mg) in March 2024, specifically to reduce the risk of cardiovascular death, heart attack, and stroke in adults with established cardiovascular disease and either obesity or overweight. This was the first time a weight-management medication received a cardiovascular-risk-reduction indication.

The American Heart Association and American College of Cardiology incorporated SELECT's findings into updated treatment algorithms, positioning semaglutide as a therapeutic option for secondary cardiovascular prevention in patients with obesity.

SELECT also reframed the clinical conversation about obesity treatment. For decades, insurers and some physicians viewed weight-loss drugs as cosmetic. A trial proving cardiovascular event reduction in a hard clinical endpoint, adjudicated by an independent committee, using an intention-to-treat analysis, carried a different kind of weight in coverage and formulary decisions.

The bottom line

SELECT established three things. First, semaglutide 2.4 mg reduces major cardiovascular events in people with obesity and existing heart disease who do not have diabetes. Second, this benefit appears additive to standard cardiovascular medications (statins, antihypertensives, antiplatelets). Third, the cardiovascular protection is likely mediated by mechanisms beyond glucose lowering alone, since participants did not have diabetes.

The 20% MACE reduction, or about a 1.5 percentage-point absolute risk reduction over roughly 3.3 years, places semaglutide in a similar range to high-intensity statin therapy for secondary prevention, though direct comparisons across trials are imprecise.

Frequently asked questions

›What does SELECT stand for?

SELECT stands for "Semaglutide Effects on Cardiovascular Outcomes in People with Overweight or Obesity." It was a phase 3, randomized, double-blind, placebo-controlled, event-driven cardiovascular outcomes trial sponsored by Novo Nordisk.

›Did participants in SELECT have diabetes?

No. Participants with type 1 or type 2 diabetes were excluded. Those with an HbA1c of 6.5% or above at screening were also excluded. This design allowed researchers to assess cardiovascular benefits independent of blood-sugar control.

›How much weight did participants lose in the SELECT trial?

Participants on semaglutide lost an average of 9.4% of body weight by week 104, compared to 0.9% on placebo. This is somewhat less than the roughly 15% weight loss seen in the STEP trials, likely because SELECT participants were older, more medically complex, and on multiple medications that can affect weight.

›Did semaglutide reduce the risk of death in SELECT?

Cardiovascular death was numerically lower in the semaglutide group (2.5% vs. 3.0%), but this difference did not reach statistical significance (HR 0.85; 95% CI 0.71 to 1.01). All-cause mortality was also not significantly different between the groups (HR 0.95).

›What were the most common side effects in SELECT?

Gastrointestinal symptoms were most common. Nausea affected about 17% of the semaglutide group (vs. 7% on placebo), diarrhea affected about 12% (vs. 8%), and vomiting affected about 8% (vs. 3%). Most of these events were mild to moderate and occurred during dose escalation.

›Does SELECT apply to people without heart disease?

Not directly. SELECT enrolled only participants with established atherosclerotic cardiovascular disease (prior heart attack, stroke, or peripheral artery disease). Whether semaglutide prevents first cardiovascular events in people without existing heart disease has not been tested in a dedicated outcomes trial.

›How does SELECT compare to SUSTAIN-6?

SUSTAIN-6 tested a lower dose of semaglutide (up to 1.0 mg) in patients with type 2 diabetes and showed a 26% MACE reduction. SELECT tested 2.4 mg in patients without diabetes. Both showed cardiovascular benefit, but in different populations and at different doses. The consistency across these trials strengthens the case that semaglutide has genuine cardiovascular-protective properties.

›Did the FDA change Wegovy's label based on SELECT?

Yes. In March 2024, the FDA approved a new indication for Wegovy to reduce the risk of major adverse cardiovascular events in adults with established CVD and BMI of 27 kg/m² or greater. This made Wegovy the first weight-management drug with an approved cardiovascular indication.

›Was the 20% MACE reduction clinically meaningful?

In absolute terms, about 1.5 fewer MACE events occurred per 100 patients treated over 3.3 years. The number needed to treat was approximately 67. For a secondary-prevention intervention added on top of already-optimized care, this effect size is comparable to several established cardiovascular therapies and was viewed by cardiologists and regulatory agencies as clinically meaningful.

›Is semaglutide the only GLP-1 drug with cardiovascular benefit in obesity?

As of the SELECT publication, semaglutide was the only GLP-1 receptor agonist with a completed cardiovascular outcomes trial specifically in people with obesity and without diabetes. Tirzepatide (a dual GIP/GLP-1 agonist) has cardiovascular outcome trials underway, but those results were not yet available when SELECT was published.

References

1. Lincoff AM, Brown-Frandsen K, Colhoun HM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes. N Engl J Med. 2023;389(24):2221-2232. PubMed
2. Wegovy (semaglutide) prescribing information. Novo Nordisk. Revised March 2024. FDA Label
3. Marso SP, Bain SC, Consoli A, et al. Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6). N Engl J Med. 2016;375(19):1834-1844. PubMed
4. Visseren FLJ, Mach F, Smulders R, et al. 2023 AHA/ACC guideline update for management of chronic coronary disease. Circulation. 2023. PubMed
5. LaRosa JC, Grundy SM, Waters DD, et al. Intensive lipid lowering with atorvastatin in patients with stable coronary disease (TNT). N Engl J Med. 2005;352(14):1425-1435. PubMed