Semaglutide or Tirzepatide for Your Heart? What a New Real-World Study Found
The question comes up in my Encinitas office almost every week now. A patient is on one of the new weight-loss shots, or thinking about starting one, and wants to know which is better for the heart, semaglutide, sold as Wegovy and Ozempic, or tirzepatide, sold as Zepbound and Mounjaro. Until recently my answer was that both protect the heart and we didn’t have a head-to-head trial to separate them. A study published earlier this year, called STEER, takes a real swing at that question, and I want to walk through it carefully, including the parts that should make you cautious. This one comes with more asterisks than the headline lets on.
What the study looked at
STEER pulled records from a large database of insurance claims. That’s a study design that looks backward at patients already started on one drug or the other by their own doctors, rather than randomly assigning them the way a clinical trial would. Researchers built two matched groups, just over 10,600 patients each, pairing semaglutide and tirzepatide patients who looked alike at the start on everything the data could measure, age, weight, other medications, prior heart history.
Everyone in the study was 45 or older, carrying extra weight, and living with established heart disease, meaning a prior heart attack, an ischemic stroke, or peripheral artery disease, the clogging of arteries in the legs. Nobody in the study had diabetes. So this is the patient who has heart disease and a weight problem, but whose blood sugar isn’t part of the picture.
The team then tracked two ways of counting cardiac trouble. One measure was tighter, counting heart attacks, strokes, and death from any cause. A wider one added hospital stays for heart failure and procedures to reopen blocked heart arteries.
What they found, and why one number is more trustworthy than the other
On the main analysis, the one that kept every patient counted in the group they started in even if they later switched drugs or stopped taking either one, semaglutide came out ahead. Patients started on semaglutide had a 29 percent lower risk of the tighter combination, heart attack, stroke, death, than patients started on tirzepatide, and a 22 percent lower risk of the wider combination. Those are real gaps if they hold up.
There’s a second version of the same analysis, one that only counted the time patients actually stayed on the drug they were first given. That version showed a much bigger gap, closer to a 57 percent lower risk on the tighter measure. I’d treat that number with real skepticism. Only counting people while they stick with a drug is a known way to flatter a result, because patients who keep taking a medication tend to be healthier and more careful about everything else, their diet, their other prescriptions, their follow-up visits, than patients who stop. That pattern alone can make a drug look better than it actually is. Those 29 and 22 percent figures are the ones I’d lean on.
There’s a second catch worth sitting with. Average follow-up was short, well under a year, about eight months for the main analysis and closer to four months for the stricter one. Heart attacks and strokes usually take years to show a real separation between two effective drugs. An eight-month real-world look is an early read, not a settled one.
Why the semaglutide finding is still worth taking seriously
Here’s the context that keeps it credible despite all that. Semaglutide has already been through a large randomized trial in almost this exact population, patients with heart disease and obesity but no diabetes. That trial followed more than 17,000 patients for over three years and found semaglutide cut the combined risk of heart attack, stroke, and cardiovascular death by 20 percent. The FDA added heart protection to Wegovy’s label on the strength of that result, and it remains the only one of these two drugs with that specific label claim.
Tirzepatide’s cardiovascular evidence sits at an earlier stage for this particular question. In patients with diabetes and heart disease, it’s been tested against another injectable diabetes drug rather than a placebo, and it met the bar for not being worse without clearly beating that comparator on the main combined outcome, though it did lower deaths from any cause in that trial. Its dedicated outcomes study in patients with obesity and no diabetes, the exact population STEER looked at, is still running and hasn’t reported results.
Why you shouldn’t take the number at face value
Now the caution I’d be doing you a disservice to skip. STEER isn’t the only real-world look at this question, and the others don’t all point the same way. A similarly designed study in patients with diabetes found essentially no difference between the two drugs on heart attack, stroke, and death risk. A separate analysis, in patients without diabetes, found the opposite direction, fewer heart-related hospitalizations on tirzepatide, driven mostly by heart failure admissions. When three studies built the same way point three different directions, none of them, STEER included, gets to be the final word.
The deeper problem is one every study like this shares. Nobody was randomly assigned to one drug or the other. Doctors and patients picked, for reasons the data can’t fully capture. Maybe the sicker patients, or the ones with better insurance, or the ones seeing more attentive doctors, tended to land on one drug over the other. Those hidden differences can create the appearance of a benefit that isn’t really about the drug. Researchers use statistical tools to level that playing field, but the tools can only adjust for what’s actually measured. A randomized trial is the only way to settle a question like this cleanly, and none exists yet for this specific comparison.
There’s also a wrinkle that surprises people. On pure weight loss, the head-to-head trial evidence favors tirzepatide, and by a real margin. In a randomized trial that compared the two drugs directly, tirzepatide patients lost about 20 percent of their starting weight over a year and a half, against about 14 percent on semaglutide, a gap of roughly six percentage points. So one drug has the edge on the scale while the other has the stronger track record, so far, on preventing heart attacks and strokes. Those can both be true at once, and it means the better drug depends on what you and I are actually trying to accomplish.
How I actually use this
None of this changes my starting point. Both of these medications help the heart, and they’re among the more useful additions to cardiometabolic care I’ve had in my years of practice. If you’re carrying extra weight and you’ve had a heart attack or a stroke, being on one of them is usually a good thing. This debate is about picking between two strong options, not about whether to treat at all.
I had a patient last spring, a man in his sixties with a stent placed two years earlier, who came in on tirzepatide because his sister-in-law had done well on it. Once we mapped out that his main problem was preventing a second heart attack, not losing his last fifteen pounds, we switched him to semaglutide. He wasn’t thrilled to give back some of the weight loss, and I told him that trade was worth it for his heart, based on what we know today.
That’s roughly where I land. When a patient’s central problem is established heart disease and the whole point is preventing the next event, this data, imperfect as it is, nudges me toward semaglutide, mostly because of its own randomized outcomes trial and because more than one real-world look points the same direction on the harder outcomes, even though not every one agrees. When the dominant problem is severe obesity and we need maximum weight loss to get diabetes, sleep apnea, or joint disease under control, tirzepatide’s stronger weight numbers pull real weight in the decision. Most of my patients, from Encinitas down through San Diego, sit somewhere in the middle, and the choice also comes down to what their insurance covers, how they tolerate the side effects, and which one they’ll actually keep taking. The best drug is the one you’ll stay on.
I also want to keep these medications in perspective. They work best as part of a plan, alongside everything else. The heart protection I count on still rests on the basics, controlling blood pressure and cholesterol, moving your body, and eating in a way that keeps your weight heading the right direction.
I go through how these drugs guard the heart beyond the weight loss in my article on GLP-1 medications and heart protection, and I cover what to realistically expect on the scale in my guide to GLP-1 medications for weight loss. For patients whose high blood sugar, wide waist, and high blood pressure travel together, the whole cluster is worth treating at once, which I describe in my piece on metabolic syndrome.
The bottom line for patients
A single real-world study, especially one this contested, doesn’t rewrite the rules, and I’d caution anyone against dropping a medication that’s working well for them on the strength of one analysis. What STEER adds is one more data point on top of a message the strongest trial evidence was already sending on the heart side, even as other real-world data cuts the other way. For a patient whose central problem is heart disease, semaglutide still has the deeper evidence behind it for preventing heart attacks and strokes. For a patient whose central problem is obesity itself, tirzepatide’s edge on weight loss still counts for a lot.
If you’re on one of these drugs, or weighing whether to start, bring this to your next visit. What are you mainly trying to accomplish, protecting your heart or losing the most weight? Which drug does your insurance actually cover? How are you tolerating what you’re on? Those questions, applied to your situation, tell you more than any single headline number. Bring them in, and we’ll pick the option that fits your heart and your life.
This post is for education and isn’t a substitute for personal medical advice. Talk with your own physician about your risk factors and what’s right for you.