GLP-1s and Cardiovascular Health: The Evidence

The question 'do GLP-1s protect the heart?' now has a real outcome-trial answer for semaglutide, a partial one for tirzepatide, and an older one for liraglutide. The answers are not the same, and the differences matter.

What did the SELECT trial actually show?

SELECT enrolled more than 17,000 adults who had overweight or obesity and established cardiovascular disease but did not have type 2 diabetes. Over roughly four years, major adverse cardiac events — cardiovascular death, heart attack, or stroke — occurred in 6.5% of the semaglutide group versus 8.0% on placebo. That is a 20% relative reduction, and about 1.5 percentage points in absolute terms.

The population is the point. Earlier GLP-1 outcome trials studied people with type 2 diabetes, so the benefit could always be attributed to better glucose control. SELECT removed that explanation. It is the first trial to show that a GLP-1 reduces cardiac events in people taking it without diabetes.

Does tirzepatide have the same evidence?

Not yet, and not in the same population. SURPASS-CVOT compared tirzepatide against dulaglutide — an active GLP-1 comparator, not placebo — in people with type 2 diabetes and cardiovascular disease. Major cardiac events occurred in 12.2% on tirzepatide versus 13.1% on dulaglutide. That met the bar for non-inferiority but not superiority: tirzepatide was not worse, but it was not proven better. On a broader cardiorenal composite it did come out ahead.

The trial that would match SELECT for tirzepatide is SURMOUNT-MMO, in people with obesity and without diabetes. It is still running. Until it reports, anyone telling you tirzepatide has SELECT-level cardiovascular evidence is ahead of the data.

What about liraglutide?

LEADER showed a cardiovascular benefit for liraglutide in people with type 2 diabetes. It is the older evidence, in the diabetes population, and liraglutide is a daily injection with smaller weight effects than the current generation.

Why would a weight-loss drug help the heart?

• Weight loss itself reduces cardiac workload and improves blood pressure.
• GLP-1s lower inflammatory markers independent of weight change.
• Blood-sugar and lipid improvements reduce atherosclerotic risk over time.
• In SELECT, the benefit appeared earlier than weight loss alone would explain — which suggests more than one mechanism is involved.

Who does this evidence actually apply to?

SELECT studied people who already had cardiovascular disease. That is a high-risk group, and absolute benefit is largest when baseline risk is high. If you are younger, have no established heart disease, and are using a GLP-1 primarily for weight, the SELECT result does not transfer directly to you — the mechanism is plausible, but the trial did not test that population.

It is also worth being explicit: every trial discussed here studied branded, FDA-approved products at studied doses. None of them studied compounded semaglutide or tirzepatide. Cardiovascular findings should not be assumed to carry over to a compounded product.