Does a Weight-Loss Drug Prevent Heart Attacks? Reading the SELECT Trial

Yes, with limits. In the SELECT trial, once-weekly semaglutide lowered the rate of major cardiovascular events by roughly 20 percent in adults who already had heart disease and carried excess weight but did not have diabetes. That result rests on a hard clinical endpoint, actual heart attacks, strokes, and cardiovascular deaths, rather than on the scale reading that usually sells these drugs. What the trial does not show is that a weight-loss medication prevents heart attacks in the general public.

What SELECT actually tested

SELECT stands for Semaglutide Effects on Cardiovascular Outcomes in People With Overweight or Obesity. Published in the New England Journal of Medicine in November 2023 by A. Michael Lincoff and colleagues, it enrolled 17,604 adults who were at least 45 years old, had a body-mass index of 27 or higher, and had survived a prior heart attack or stroke or lived with symptomatic peripheral artery disease. None had diabetes at entry. Participants received either weekly injectable semaglutide or a matching placebo and were followed for a mean of roughly 40 months. The primary endpoint was a composite of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke, the cluster clinicians call MACE.

This mattered because the earlier cardiovascular-outcome trials for this class of drug had been run mostly in people with type 2 diabetes, where any heart benefit could plausibly be tied to better glucose control. SELECT removed diabetes from the picture. By enrolling only participants without it, the trial isolated the question of whether the medication protected hearts in obesity on its own terms, and it stands as the first large trial to answer yes for this class in a nondiabetic population.

A hard outcome, not a surrogate

Most coverage of these medicines reports one thing: weight. Weight is a surrogate endpoint, a measurable stand-in that we hope moves in step with the outcomes patients actually care about. A drug can shift a surrogate impressively and still fail to change lives, or even cause harm, which is why regulators and trialists treat surrogates with caution. SELECT was built to answer the harder question of whether the drug reduced the events themselves. Because the answer came from counting strokes and heart attacks rather than pounds, its evidentiary weight differs in kind from a weight-loss study.

Reading the numbers

A primary event occurred in 6.5 percent of the semaglutide group versus 8.0 percent on placebo, a hazard ratio of 0.80 (95 percent confidence interval, 0.72 to 0.90; P less than 0.001). That is a 20 percent relative reduction and an absolute difference of about 1.5 percentage points across the trial, which works out to roughly one event avoided for every 67 people treated over nearly three and a half years. Among the three components, nonfatal myocardial infarction fell most clearly, with a hazard ratio near 0.72. Cardiovascular death showed a smaller, statistically uncertain signal, and nonfatal stroke pointed the same way without standing on its own. The composite benefit is real; several of its parts, examined alone, are less certain, and an honest reading holds both facts at once.

Weight loss versus heart protection

Participants on semaglutide lost about 9.4 percent of body weight against 0.9 percent on placebo, and a later Nature Medicine analysis found that this weight loss continued to accumulate for more than a year and was sustained for up to four years. It is tempting to conclude that the weight drove the heart benefit, yet the trial cannot support that leap. The event curves began separating early, before much weight loss had accumulated, and the drug also lowered blood pressure, reduced inflammatory markers, and cut the onset of new diabetes. As the American College of Cardiology summary noted, the cardioprotective mechanism is most likely multifactorial, and crediting weight loss alone overreads the data.

Who the result applies to

SELECT describes a specific population: middle-aged and older adults with established cardiovascular disease and excess weight but no diabetes. This is secondary prevention, treating people who have already had an event. The trial says nothing certain about a healthy person with a high BMI and no heart disease, and nothing about using the drug purely for cosmetic weight loss. Stretching a secondary-prevention result to primary prevention, or to the general consumer market, is precisely the inferential jump the study was not designed to make. Who a result applies to is defined by who was enrolled, and the enrollment here was narrow and deliberately high-risk.

Weighing benefit against cost

Benefit arrived with cost. Adverse events leading to permanent discontinuation occurred in 16.6 percent of the semaglutide group versus 8.2 percent on placebo, driven mostly by gastrointestinal intolerance, according to the NEJM report. The trial was funded by the drug's manufacturer, a common arrangement that careful readers factor into their appraisal rather than wave away. None of this negates the finding; it frames it. A 20 percent reduction in hard events is a genuine advance for the population studied, and it is also a modest absolute shift bought with real side effects and real dropout.

The larger lesson outlasts this one molecule. When a product is marketed on how much weight it removes, the useful question is whether anyone has shown it changes the outcomes that weight is supposed to predict. SELECT did that work for one drug in one high-risk group, and the discipline it models, separating a hard endpoint from a flattering surrogate and asking exactly whom the data cover, is worth applying to the next headline. This article is educational and not medical advice; decisions about any medication belong with a qualified clinician who knows the individual.