Semaglutide appears to protect patients from serious cardiovascular events through effects beyond weight loss. A new analysis of the international SELECT trial found that changes in body weight and waist size cannot fully explain the drop in cardiovascular events and vascular deaths, including heart attacks and strokes. The missing mechanism remains one of the basic scientific questions around Ozempic and Wegovy.
The finding is unusually clear: conventional explanations account for no more than half of the benefit seen in the trial.
Published in the European Heart Journal, the analysis examined 17,604 adults with overweight or obesity, established cardiovascular disease and no diabetes. Participants received a weekly 2.4-milligram dose of semaglutide or a placebo and were followed for about four years. Researchers tracked changes in body weight and blood pressure, along with cholesterol. They also monitored inflammation markers and kidney function, then tested how much those changes could explain the cardiovascular results. The analysis used the SELECT population, not a separate trial.
Every major measure improved in the treated group. Even so, those measures did not explain the full drop in risk, whether researchers looked at them together or separately. Helen Colhoun of the Universidad de Edinburgo said the available analysis could not link semaglutide's cardiovascular effect to known risk factors "with total certainty." The drug's clinical effect so reaches beyond the mechanisms most often used to explain obesity-related heart disease.
The original SELECT trial found a 20% reduction in major adverse cardiovascular events: 6.5% of participants in the semaglutide group experienced such an event, compared with 8.0% in the placebo group, corresponding to a hazard ratio of 0.80. The new analysis examines why conventional changes in risk factors cannot fully account for that benefit.
That changes how doctors may read the treatment's results. Weight loss remains an impressive effect, but the data do not show that it alone explains why patients have fewer major cardiovascular events. Expert commentary collected by the Science Media Centre also describes a large part of the benefit as unexplained by standard surrogate measures.
Researchers are considering several possible explanations. Semaglutide may lower inflammation in tissues or improve the endothelium, the lining of blood vessels. It may also directly protect the heart muscle. The analysis did not establish any of these explanations. Together, they show why the cardiovascular result cannot be reduced to a smaller waistline.
Andreu Palou of the Universitat de Islas Baleares also says weight loss is not enough to explain the protection seen in the trial. Cristóbal Morales leads the Unidad de Salud Metabólica, Diabetes y Obesidad at Hospital Vithas Sevilla and coordinates SELECT in Spain. He said improvements in weight and inflammation account for only part of the effect. Changes in glucose control and blood pressure do as well.
Morales sees the result as evidence that semaglutide has a role beyond slimming treatment. The drug class has reduced major cardiovascular events by about 20%, information from material presented with the study. In outside discussions of the analysis, roughly 69% of the observed effect is described as needing further investigation. That figure is an interpretation of the mediation analysis, not proof of one additional biological mechanism. The evidence points to a wider clinical role focused on vascular protection, with implications beyond appearance.
The question matters to patients and families making long-term treatment decisions. It also comes alongside other pressures affecting household choices in Spain, including those covered in the earlier housing analysis. The medical evidence here, though, concerns cardiovascular outcomes rather than household finances.
The regulatory stakes have also grown. After the SELECT findings, the U.S. Food and Drug Administration expanded Wegovy's indication to reduce the risk of major cardiovascular events in adults with established cardiovascular disease and overweight or obesity. The decision rests on demonstrated outcome data. It does not mean that every biological pathway has been identified.
An editorial accompanying the study was written by cardiac surgeon Subodh Verma and colleagues at the Universidad de Toronto. They argue that incomplete knowledge of the biological pathway should not prevent therapeutic use. Medicine often relies on demonstrated outcomes before every molecular detail is known. The missing mechanism still matters: finding it could help doctors refine treatment and identify which patients receive the greatest protection. The SELECT data show that semaglutide's cardiovascular benefit is real, while the biology behind it remains unfinished science.
