The SUMMIT trial tirzepatide results come down to one clear finding and one important catch. In a trial of 731 adults with obesity and a stiff-heart form of heart failure, people given a weekly tirzepatide shot had a 38% lower combined risk of dying from a heart cause or having heart failure get worse than people given a placebo shot: 9.9% against 15.3%, over a median of two years. The catch is that nearly all of the gap came from fewer heart-failure flare-ups, not fewer deaths, and no U.S. label lists heart failure as a use.
The condition is HFpEF, short for heart failure with preserved ejection fraction. The ejection fraction is the share of blood the heart pushes out with each beat. In HFpEF that number looks normal, but the muscle has grown stiff, so the heart fills poorly and pressure backs up into the lungs. Breathlessness, swollen ankles and tiring quickly are typical, and excess weight is one of the strongest drivers.
What question did the SUMMIT trial ask?
SUMMIT asked whether tirzepatide could cut heart-failure events and ease symptoms when HFpEF comes with obesity.
It was a phase 3 trial, the large late-stage kind designed to confirm a result. It was randomized, meaning chance decided who got which shot, and double-blind, meaning neither participants nor their doctors knew. Milton Packer and colleagues published it in the New England Journal of Medicine in January 2025; the ClinicalTrials.gov record is NCT04847557. Eli Lilly, which makes tirzepatide, paid for it.
Who was enrolled, and for how long?
Everyone had heart-failure symptoms, an ejection fraction of 50% or higher, a BMI of at least 30, and evidence of heart strain, such as a raised NT-proBNP, a blood marker the heart releases under pressure.
The average participant was 65, and 54% were women. Average BMI was 38.2, and 48.2% had type 2 diabetes. Three in four already took a diuretic, a water pill that helps the body shed extra fluid. The trial left out people with a major heart event in the previous 90 days, poorly controlled diabetes, a history of pancreatitis, or kidney failure needing dialysis.
Tirzepatide was stepped up toward 15 mg once a week, stopping at the highest dose each person tolerated. Those were the trial's rules, not a plan for anyone reading; a prescriber sets an individual's dose. Treatment lasted at least 52 weeks, and median follow-up was 104 weeks.
How the trial measured success
SUMMIT had two primary endpoints, the main results chosen before it began.
The first was the time until cardiovascular death or a worsening heart-failure event: a hospital stay, an urgent visit needing intravenous treatment, or a doctor raising the diuretic dose because heart failure got worse. An independent committee checked each one.
The second was the change at 52 weeks on the KCCQ, the Kansas City Cardiomyopathy Questionnaire. It is a 23-question survey about symptoms and physical limits, scored 0 to 100, where higher is better.
What the SUMMIT trial tirzepatide results showed
| Measure | Tirzepatide | Placebo | Between groups |
|---|---|---|---|
| Cardiovascular death or worsening heart failure | 36 of 364 (9.9%) | 56 of 367 (15.3%) | HR 0.62 (0.41–0.95) |
| Worsening heart-failure events | 29 (8.0%) | 52 (14.2%) | HR 0.54 (0.34–0.85) |
| Cardiovascular death | 8 (2.2%) | 5 (1.4%) | HR 1.58 (0.52–4.83) |
| KCCQ change at 52 weeks | +19.5 points | +12.7 points | 6.9 points |
| Six-minute walk change at 52 weeks | +26.0 m | +10.1 m | 18.3 m |
| Body weight change at 52 weeks | −13.9% | −2.2% | −11.6 points |
A hazard ratio (HR) compares how often something happens over time in two groups, so 0.62 means about 38% lower risk. The numbers in parentheses are the 95% confidence interval, the range the true value most plausibly sits in. For the main endpoint that range stays below 1. For cardiovascular death it runs from well below 1 to well above it, so it says almost nothing either way.
Put simply, about 1 in 10 people on tirzepatide had one of these events, against about 3 in 20 on placebo. The event and KCCQ figures are the paper's; the walk and weight figures are from the results Lilly posted to the trial registry.
What drove the result: flare-ups, not deaths
A combined endpoint can hide which part did the work. Here it was heart-failure events. The European Medicines Agency's scientific committee broke them down in its January 2026 assessment report: hospital admissions for heart failure in 12 people on tirzepatide (3.3%) against 26 on placebo (7.1%), urgent visits in 5 against 12, and diuretic increases in 17 against 21.
Deaths went slightly the other way, though the numbers are small: 8 against 5 from heart causes, and 19 against 15 from any cause. That is far too few for SUMMIT to say whether tirzepatide changes survival in either direction.
The same report noted that counting diuretic increases, a softer event than a hospital stay, could "soften" the endpoint, then concluded that this piece "did not relevantly contribute to the overall result". With it removed, the main result held, at a hazard ratio of 0.57.
Side effects reported
Most side effects were the familiar stomach and bowel ones, and they peaked early. Nausea, diarrhea or vomiting affected 13.7% of the tirzepatide group in weeks 4 to 8; after week 20 it stayed under 9% in every period measured.
| Event, any time in the trial | Tirzepatide | Placebo |
|---|---|---|
| Diarrhea | 18.4% | 6.3% |
| Nausea | 17.0% | 6.5% |
| Constipation | 14.8% | 6.0% |
| Vomiting | 10.4% | 2.2% |
| Dizziness | 9.3% | 4.9% |
| Low blood pressure | 6.0% | 3.0% |
| Stopped the study drug because of a side effect | 6.3% | 1.4% |
The last row is from the paper; the rest are from the European report's safety table. Dizziness and low blood pressure matter more here than in a weight-loss trial, because most participants already took diuretics and blood-pressure-lowering heart drugs.
What regulators and later studies said
United States. Lilly's quarterly report for early 2025 states that it withdrew its U.S. application for tirzepatide in HFpEF. As of September 22, 2026, the day this article was written, neither U.S. tirzepatide label lists heart failure. The Zepbound label (Revised: 8/2026) covers weight reduction and obstructive sleep apnea. The Mounjaro label (Revised: 8/2026) added heart wording in August 2026, but it is about heart attack, stroke and cardiovascular death in type 2 diabetes, from a different trial covered in tirzepatide's heart evidence.
Europe. The committee's report, dated 29 January 2026, turned down a separate heart-failure indication. People with HFpEF and obesity already qualify under the weight-management indication, it reasoned; tirzepatide "was not able to reduce CV mortality"; and uncertainty remains on whether the benefit is "independent from weight loss". The results went into the product's clinical-data section instead.
Guidelines. Doctors' societies went further: on August 28, 2026, the European Society of Cardiology gave semaglutide or tirzepatide a Class IIa, "should be considered", recommendation for preserved ejection fraction with obesity; our guide to the 2026 heart-failure guidelines covers who that includes.
Later analyses. As of September 22, 2026, the day this article was written, the newest SUMMIT paper is a planned analysis by sex, published July 7, 2026: the benefit looked similar in women and men, with hazard ratios of 0.66 and 0.61 (Borlaug et al., JACC: Heart Failure 2026). A 2025 insurance-claims study found no meaningful difference between people starting tirzepatide and people starting semaglutide on heart-failure hospitalization or death, at a hazard ratio of 0.86 (0.70–1.06) (Krüger et al., JAMA 2025). Claims data can show an association, not prove cause. Semaglutide's own trials are in semaglutide for heart failure.
What SUMMIT cannot say about a compounded version
SUMMIT studied Lilly's tirzepatide, given under a trial protocol to people whose heart failure was confirmed and tracked by cardiologists. It did not test compounded tirzepatide. Through Promise, tirzepatide is dispensed as a compounded medication, which is different from an FDA-approved product: the formulation offered here is not FDA-approved and carries no heart-failure indication. The FDA explains that it does not verify a compounded drug's safety, effectiveness or quality before it is sold; what compounded tirzepatide is walks through the difference.
A licensed provider may still prescribe a compounded formulation when they judge it appropriate; that decision is between you and your doctor. At Promise, a licensed provider reviews every request, and not everyone qualifies. When heart failure is part of the history, weight treatment sits alongside heart-failure care rather than replacing it, and the prescriber and cardiologist need the same medication list.
Reading SUMMIT fairly
SUMMIT is the main randomized evidence so far for tirzepatide in obesity-related HFpEF, and its differences from placebo were in flare-ups, symptoms, walking distance and weight. It did not show longer survival, it enrolled only people with a BMI of 30 or more, and it left open how much of the benefit is the weight loss itself. Kept attached to those limits, it is a good reason for a conversation with a cardiologist, not a promise.