For years, the case for treating obesity rested largely on the scale and on surrogate markers — blood pressure, lipids, blood sugar. The SELECT trial changed the terms of that argument. It asked a harder question: in people who carry excess weight and already have heart disease but not diabetes, does semaglutide actually prevent heart attacks, strokes, and cardiovascular deaths? The answer, published in the New England Journal of Medicine in 2023, is what turned a weight drug into a cardiovascular one — and it is the evidence behind Wegovy's FDA cardiovascular-risk-reduction indication.[1]
Why SELECT mattered
Semaglutide had already been shown to cut cardiovascular events in people with type 2 diabetes, and the STEP program had established that the 2.4 mg dose produces large weight loss. But those are different claims. Weight loss and better lab numbers are worth having, yet regulators, payers, and clinicians ultimately want to know whether a drug keeps people alive and out of the hospital. SELECT was designed to test exactly that in a population where the question had never been answered: overweight or obese adults with heart disease but without diabetes.[1]
How the trial was built
SELECT was a multicenter, double-blind, randomized, placebo-controlled, event-driven superiority trial. It enrolled 17,604 patients, each at least 45 years old, with a body-mass index of 27 or greater, preexisting cardiovascular disease (a prior heart attack, prior stroke, or symptomatic peripheral arterial disease), and no history of diabetes. Participants were randomized 1:1 to once-weekly subcutaneous semaglutide 2.4 mg (8,803 people) or matching placebo (8,801 people), on top of standard cardiovascular care. The mean duration of follow-up was 39.8 months — a little over three years. The primary endpoint was a composite, time-to-first-event measure of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke — the conventional three-point MACE.[1]
The primary result
A primary endpoint event occurred in 569 of 8,803 patients (6.5%) on semaglutide and in 701 of 8,801 patients (8.0%) on placebo. That works out to a hazard ratio of 0.80 (95% CI 0.72 to 0.90; P<0.001) — a roughly 20% relative reduction in the risk of a major cardiovascular event.[1] It was the first randomized evidence that a medication given primarily for weight could change hard cardiovascular outcomes in people without diabetes. A prespecified analysis later confirmed that the accompanying weight loss — about 10.2% versus 1.5% on placebo — built over the first year and was sustained for up to four years.[2]
Safety and discontinuation
The trade-off shows up in tolerability. Adverse events leading to permanent discontinuation of the trial product occurred in 16.6% of the semaglutide group versus 8.2% of the placebo group (P<0.001) — roughly twice as many, driven mainly by the gastrointestinal effects characteristic of GLP-1 receptor agonists.[1] Serious adverse events overall were not more frequent on semaglutide; in the weight-focused analysis they were somewhat lower across BMI categories.[2] Still, one in six people stopping the drug for side effects is a real signal about who can stay on it long enough to benefit.
The honest limitations
The relative 20% reduction is genuine, but the absolute benefit is modest: an event rate of 6.5% versus 8.0% is about 1.5 fewer events per 100 people spread over more than three years. Framed as number-needed-to-treat, that is on the order of dozens of people treated for several years to prevent one event — meaningful at population scale, less dramatic for any single person than the headline percentage suggests.[1] Second, the mechanism is not fully understood: the degree of weight loss did not neatly track with the size of the cardiovascular benefit, which points to effects on inflammation, blood pressure, and the vessel wall that go beyond the scale.[2]Third, generalizability is bounded — everyone in SELECT already had established heart disease, so the results do not directly speak to primary prevention in lower-risk people. Finally, there is cost and access: sustained benefit requires sustained treatment, and the drug is expensive and, in many places, hard to obtain.
What it means
SELECT reframed semaglutide as a cardiometabolic therapy rather than a cosmetic one, and it is the clinical foundation for how these drugs are now positioned. It also sharpens the comparisons buyers actually make — how the 2.4 mg semaglutide dose behind Wegovy stacks up against Zepbound, and how semaglutide compares with tirzepatide more broadly. The key caveat: tirzepatide has not yet reported a comparable dedicated cardiovascular-outcomes trial in this population, so a like-for-like MACE comparison does not exist. SELECT tells us that, for people with obesity and established heart disease, semaglutide does more than move the number on the scale — but the effect is a measured one, and it is not a substitute for personalized medical advice.