Issue 5: June 2, 2026

This week

The biggest unanswered question in obesity pharmacology just got a real answer: in head-to-head data, tirzepatide and semaglutide reduce cardiovascular events at similar rates, even though tirzepatide produces meaningfully more weight loss. We break down what the new Nature Medicine real-world analysis and the SURMOUNT-5 post-hoc actually show, the dosing framework for choosing between the two, why adding GIP receptor agonism may not produce additive cardiovascular benefit, and the public comment deadline for the PCAC peptide review that is six weeks away.

Study of the Week

Tirzepatide and Semaglutide Tied on Cardiovascular Outcomes: What the Real-World Comparison Actually Shows

The standard framing of tirzepatide versus semaglutide has been settled for two years: tirzepatide produces more weight loss. SURMOUNT-5, the first Phase 3 head-to-head, made this clear. What has not been settled, until now, is whether that weight-loss advantage translates into a cardiovascular outcomes advantage. Two new analyses, both published in late 2025, suggest it does not.

The first is a real-world cohort study published in Nature Medicine in November 2025 by Krueger and colleagues at Brigham and Women's Hospital and Harvard Medical School. The team used US insurance claims data from 2018 to 2025 to emulate two cardiovascular outcome trials: SUSTAIN-6 (semaglutide versus sitagliptin) and SURPASS-CVOT (tirzepatide versus dulaglutide). They then conducted a direct head-to-head comparison of semaglutide and tirzepatide in patients with elevated cardiovascular risk.

The result: in the direct head-to-head comparison, the hazard ratio for tirzepatide versus semaglutide was 1.06 (95% confidence interval 0.95 to 1.18). The confidence interval crosses 1.0, meaning the difference is not statistically significant. But the point estimate trends slightly in semaglutide's favor, not tirzepatide's. The cleanest reading: tirzepatide and semaglutide produce similar cardiovascular event reductions in real-world use. Tirzepatide is not superior. If anything, the data hints at the opposite.

The second is a post-hoc analysis of SURMOUNT-5, the Phase 3 trial that directly compared the two compounds at maximum tolerated doses in adults with obesity. Mamas and colleagues, publishing in European Heart Journal Open in September 2025, modeled 10-year cardiovascular disease risk based on the changes in cardiometabolic risk factors observed in SURMOUNT-5. The model projected approximately 70 fewer new cases of type 2 diabetes and 10 fewer cardiovascular events per 1,000 patients on tirzepatide compared with semaglutide at max tolerated doses, over a 10-year horizon. Read that carefully: these are modeled projections from a risk equation, not observed cardiovascular outcomes from a trial. They depend entirely on the assumption that improvements in surrogate markers translate proportionally to hard endpoints, which they often do not in real life.

Two things to flag prominently. First, the Mamas et al. analysis has six Eli Lilly co-authors. Lilly makes tirzepatide. This is industry-funded modeling work that favors the sponsor's compound. It is not invalid, but it requires the disclosure most coverage leaves out. The Krueger et al. real-world study, by contrast, is academic, conducted by Brigham and Women's pharmacoepidemiology group with no listed pharmaceutical funding. When those two evidence sources point in different directions, the academic real-world data should carry more weight than the industry-funded model.

Second, semaglutide has the longer cardiovascular outcomes track record. SUSTAIN-6 (Marso et al., 2016, NEJM) showed a 26 percent relative reduction in major adverse cardiovascular events in type 2 diabetes, with primary endpoint events in 6.6 percent of semaglutide patients versus 8.9 percent on placebo, hazard ratio 0.74 (95% CI 0.58 to 0.95). SELECT (Lincoff et al., 2023, NEJM) showed a 20 percent reduction in nondiabetic adults with established cardiovascular disease and obesity, with a primary endpoint event in 6.5 percent of the semaglutide group versus 8.0 percent of placebo, hazard ratio 0.80 (95% CI 0.72 to 0.90), n=17,604. Tirzepatide's SURPASS-CVOT (2025) showed noninferiority to dulaglutide, which itself has established cardiovascular benefit. So tirzepatide's cardiovascular benefit is real but inherited through a noninferiority margin, while semaglutide's is established through direct placebo comparison.

The bottom line: tirzepatide produces more weight loss; in cardiovascular outcomes the two are roughly tied, with semaglutide having the longer evidence base. Anyone telling you tirzepatide is unambiguously better for cardiovascular protection is either selling something or has not read the head-to-head data.

For research and educational purposes only · Not medical advice · Consult a qualified physician before any human use