Tirzepatide vs. semaglutide for heart health: what a real-world study of 297,842 patients found

A Nature Medicine study of 297,842 patients found comparable cardiovascular outcomes for tirzepatide vs. semaglutide. What that means and what it doesn't.

We already know tirzepatide (Zepbound/Mounjaro) produces greater average weight loss than semaglutide (Wegovy/Ozempic) in head-to-head trials. What we don't yet know from randomized clinical trials is whether tirzepatide is better, worse, or equivalent for heart health. A large observational study published in Nature Medicine in 2025 is the most direct attempt so far to answer that question.

The answer the study found: comparable. But that word requires explanation.

Heart disease is the leading cause of death for people with type 2 diabetes. GLP-1 receptor agonists were originally developed to treat blood sugar and were later found to reduce cardiovascular risk in certain populations.

Multiple randomized trials have established that semaglutide reduces MACE in people with elevated cardiovascular risk. Tirzepatide's cardiovascular evidence has been emerging, and no randomized trial has directly compared the two drugs on heart outcomes. Krüger et al. conducted what is now the largest real-world head-to-head cardiovascular comparison between the two drugs, published in Nature Medicine in 2025.

The study used data from three national US insurance databases covering 2018 to 2025: Medicare Parts A/B/D, Optum Clinformatics, and Merative MarketScan.

This was an observational study — not a randomized controlled trial. That distinction matters.

In an RCT, patients are randomly assigned to treatments, which balances known and unknown differences between groups. In an observational database study, researchers look at who actually took each drug and what happened to them. To reduce the impact of differences between those groups — for example, if sicker patients were more likely to be prescribed one drug — the researchers used propensity score matching, a statistical technique that adjusts for measured characteristics.

The head-to-head comparison included 297,842 total initiators, with 172,382 in the propensity score–matched cohort that formed the basis of the primary analysis. Before analysis, the researchers validated their methods by emulating two prior randomized cardiovascular trials (SUSTAIN-6 and SURPASS-CVOT) to confirm their approach produced results consistent with known trial outcomes.

The primary outcome was a composite of heart attack (myocardial infarction), stroke, or all-cause death over one year of follow-up.

In the direct head-to-head comparison, the 1-year risk of this composite was 1.3% for both tirzepatide and semaglutide users. The hazard ratio was 1.06 (95% CI 0.95 to 1.18).

A hazard ratio of 1.06 means tirzepatide users had a 6% relatively higher event rate in this study. But the confidence interval — 0.95 to 1.18 — crosses 1.0, meaning this difference is not statistically significant. The data are compatible with no difference between the two drugs.

For individual components: HR for all-cause mortality was 1.03 (95% CI 0.84 to 1.27); for heart attack, 1.03 (95% CI 0.88 to 1.21); for stroke, 1.15 (95% CI 0.92 to 1.45). None reached statistical significance.

A secondary endpoint looked at heart failure hospitalizations. For tirzepatide vs. semaglutide, the hazard ratio was 0.91 (95% CI 0.81 to 1.01) — a modest numerical advantage for tirzepatide.

This CI also overlaps 1.0, meaning it does not reach statistical significance. The study authors note this is "consistent with recent data supporting protective effects of semaglutide and tirzepatide on heart failure outcomes and a potential incremental benefit" with tirzepatide, while acknowledging uncertainty.

The dual GIP/GLP-1 mechanism of tirzepatide may have different effects on heart failure biology than GLP-1 alone, but the authors note that current understanding of GIP's cardiovascular biology "is limited, and findings in preclinical and clinical studies point in different directions."

The study also compared each drug against older reference comparators, finding:

• Semaglutide vs. sitagliptin (a placebo proxy): HR 0.82 (95% CI 0.74 to 0.91) — a statistically significant reduction in heart attack or stroke
• Tirzepatide vs. dulaglutide (an older GLP-1 receptor agonist): HR 0.87 (95% CI 0.75 to 1.01) — numerically favorable, CI overlaps null

These findings are consistent with what prior randomized trials showed for semaglutide, and support tirzepatide's cardiovascular benefit relative to older alternatives.

All patients had type 2 diabetes and obesity, and were enrolled in US insurance programs. Mean age ranged from 59.2 to 69.2 years in the matched cohort; about half were women.

This study does not apply to:

• People without type 2 diabetes using GLP-1 medications only for weight loss
• People with obesity who do not have elevated cardiovascular risk
• Populations outside the US, or uninsured populations

Weight loss data from SURMOUNT-5 and similar trials — which showed greater weight loss with tirzepatide vs. semaglutide — is a separate question from heart outcomes. Greater weight loss does not automatically translate to better cardiovascular protection.

• A head-to-head randomized cardiovascular trial comparing tirzepatide and semaglutide directly has not yet reported results
• Whether the modest heart failure signal for tirzepatide would replicate in a larger or differently designed study is unknown
• Long-term cardiovascular data beyond one year from this study are limited
• Whether these findings apply to people using these drugs for obesity without type 2 diabetes has not been studied

• Given my cardiovascular history, is there a clinical reason to prefer one drug over the other?
• If heart failure is a concern for me, how should I weigh this study's signal?
• What ongoing cardiovascular monitoring would you recommend for someone on a GLP-1?
• Are there randomized cardiovascular trials I might qualify for?

Medical disclaimer: This content is for educational purposes only and is not medical advice. Always consult a licensed healthcare professional before starting, stopping, or changing any treatment.

Sources

• Krüger N et al. Cardiovascular outcomes of semaglutide and tirzepatide for patients with type 2 diabetes in clinical practice. Nature Medicine, 2025. nature.com
• ClinicalTrials.gov NCT06659744: clinicaltrials.gov