Semaglutide Cuts Heart Risk 29% More Than Tirzepatide

The STEER study, published in Diabetes, Obesity and Metabolism and re-circulated this week through major cardiology outlets, dropped a result that flips a common assumption. In a real-world cohort of insured US patients with obesity and established cardiovascular disease but no diabetes, semaglutide reduced major adverse cardiovascular events 29% more than tirzepatide. For per-protocol adherers, the gap widened to 57%.

This is the first head-to-head comparison of these two on cardiac outcomes — and it points the opposite direction from where the weight-loss data points.

What STEER Actually Measured

STEER is a retrospective observational cohort study using US insurance claims. The investigators identified 64,000+ adults aged 45 or older with overweight or obesity and atherosclerotic cardiovascular disease (prior heart attack, stroke, or peripheral artery disease) but no diabetes diagnosis, who initiated semaglutide or tirzepatide between May 2022 and January 2025.

The primary endpoint was 3-point MACE: cardiovascular death, non-fatal heart attack, or non-fatal stroke.

Headline Numbers

• Intention-to-treat 3-point MACE: semaglutide associated with 29% lower risk versus tirzepatide (statistically significant)
• Intention-to-treat 5-point MACE: semaglutide associated with 22% lower risk (statistically significant)
• Per-protocol 3-point MACE: 57% lower risk for semaglutide
• Per-protocol 5-point MACE: 43% lower risk for semaglutide
• Absolute event rates: 0.1% (15 events) on semaglutide vs 0.4% (39 events) on tirzepatide

The per-protocol numbers count only patients who actually stayed on their assigned drug. The intention-to-treat numbers include everyone regardless of switching or stopping — closer to what real prescribing looks like.

Why This Result Was Unexpected

Tirzepatide produces ~50% more weight loss than semaglutide in head-to-head trials (SURPASS-2, SURMOUNT-5). The reasonable assumption: more weight loss equals more metabolic improvement equals fewer heart attacks.

STEER says no.

The most likely explanation is that GLP-1 receptor activation on vascular endothelium, atherosclerotic plaques, and inflammatory pathways drives most of the cardio benefit — and that benefit doesn't scale linearly with weight loss. GIP receptor activity (the second receptor tirzepatide hits) appears to add appetite suppression and weight-loss potency without adding the same vascular protection on top.

Semaglutide already had two dedicated cardiovascular outcome trials before STEER:

• SELECT (2024): 20% MACE reduction in obesity without diabetes (HR 0.80, p<0.001)
• SUSTAIN-6 (2016): 26% MACE reduction in type 2 diabetes at high cardiovascular risk

Tirzepatide's only cardiovascular outcome trial — SURPASS-CVOT — showed non-inferiority versus dulaglutide (12.2% vs 13.1% event rate) but never tested against semaglutide directly. STEER fills that gap, even if the design is observational rather than randomized.

What This Means If You're Choosing Between Them

This is the practical decision tree for someone reading this and deciding which peptide to run.

Choose Semaglutide If

• You have established cardiovascular disease (prior heart attack, stroke, stent, peripheral artery disease)
• You're over 50 with multiple cardiovascular risk factors (hypertension, high LDL, smoking history, family history)
• You've already lost most of the weight you want to lose and you're switching from short-term weight loss to long-term metabolic protection
• You want the longest-running real-world safety data on a GLP-1

Choose Tirzepatide If

• Your primary goal is maximum weight loss in the shortest timeframe
• You don't have established cardiovascular disease
• You've plateaued on semaglutide and need stronger appetite suppression
• You tolerate tirzepatide better (some people get less GI upset on dual agonism)

What's Still Available After the FDA Crackdown

503A compounding pharmacies continue to prepare both peptides for documented medical need. The FDA's April 2026 ingredient restrictions targeted misleading telehealth marketing, not legitimate compounding. For research-grade peptides:

• Best semaglutide vendors — ranked by price, COA, reputation
• Best tirzepatide vendors — dual-agonist vendor scores
• Semaglutide vs tirzepatide head-to-head — full comparison on weight loss, sides, cost
• All vendor discount codes — current coupon round

The Limits of Observational Data

STEER is not a randomized trial. The patients who chose semaglutide differ in unmeasured ways from those who chose tirzepatide — that's the core problem with claims-based cohorts. The study used propensity score matching to balance the obvious confounders (age, sex, comorbidities, prior medications), but unmeasured selection bias remains.

A few things to keep in mind before treating these numbers as gospel:

1. Absolute event rates were small. 15 events vs 39 events sounds large in relative terms but reflects short follow-up and a generally healthy outpatient population. The 95% confidence intervals are wider than the headline percentages suggest.
2. Per-protocol analyses inflate effect sizes. People who stay on a drug long-term tend to be healthier and more compliant in general. The 57% number is impressive but the 29% intention-to-treat figure is the more accurate summary.
3. Tirzepatide is newer. Patients in this cohort had less time on tirzepatide than on semaglutide, which may have under-counted late events.
4. No randomization, no blinding. A definitive answer needs SURMOUNT-MMO or a direct head-to-head CVOT. Neither exists yet.

What STEER does prove is that the assumption "more weight loss = better cardiac outcomes" doesn't hold in this comparison. That's a meaningful update.

How This Fits With the Other 2026 GLP-1 News

This year has been brutal for the "tirzepatide is just better" narrative.

• REDEFINE 4 (February 2026): CagriSema came within 2.5 percentage points of tirzepatide on weight loss (23.0% vs 25.5%) — closing the gap that semaglutide alone couldn't close
• ATTAIN-MAINTAIN (December 2025): oral orforglipron successfully maintained weight loss when patients switched from injectable semaglutide or tirzepatide
• AD/PD 2026: semaglutide failed to slow early Alzheimer's disease in EVOKE/EVOKE+, but real-world data still shows 40-70% lower dementia diagnosis rates in type 2 diabetes
• TRIUMPH-4 (Q1 2026): retatrutide hit 28.7% weight loss with 75.8% knee pain reduction — but no cardiovascular outcomes data
• STEER (this study): semaglutide beats tirzepatide on heart events 29-57%

The pattern: tirzepatide owns weight loss, semaglutide owns cardiovascular protection, retatrutide owns the future of weight loss without cardiovascular data yet, and orforglipron owns convenience.

The Bottom Line

If you have heart disease and obesity without diabetes, semaglutide is the better-evidenced choice — STEER added 29% lower MACE on top of SELECT's existing 20%. If you don't have heart disease and you want maximum weight loss, tirzepatide still wins on the scale.

Don't switch protocols based on a single observational study. Do bring this up with your prescriber if you're on tirzepatide and you have a prior heart attack or stroke. The mechanism makes biological sense — and the cardiovascular outcome trial gap between these two drugs is no longer theoretical.