The September headlines don't settle Zepbound vs Wegovy HD. Neither announcement reports a trial that directly assigned people to those two obesity treatments. Lilly compared weight loss across separate obesity trials. Novo studied heart-related outcomes after people with diabetes changed treatment.
As of September 30, 2026, the day this article was written, both companies had announced analyses on September 29 at EASD, a diabetes research meeting. Lilly's announcement favors Zepbound for weight. Novo's announcement favors increasing Ozempic over switching to Mounjaro for its measured outcomes. Neither settles which treatment suits a particular person.
Zepbound vs Wegovy HD: what changed
Wegovy HD is the 7.2 mg semaglutide injection. Zepbound contains tirzepatide. The FDA's March 19, 2026 decision added Wegovy HD for weight management in certain adults. The broader differences between the brands are covered in Zepbound vs Wegovy.
Lilly's September comparison joins SURMOUNT-1, which tested tirzepatide, to STEP UP, which tested semaglutide. Both followed adults without diabetes for 72 weeks. An indirect treatment comparison estimates a difference between medicines studied in separate trials, using a shared comparison such as placebo, a dummy injection.
A model tries to account for differences between the study populations. That helps, but it cannot recreate assigning people randomly between the two medicines in one trial.
Why Lilly reported two weight-loss gaps
An estimand is the question a study's analysis is designed to answer. Change that question and the number can change too. Our estimand explainer covers the names researchers use.
The treatment-regimen analysis includes treatment stops. The efficacy analysis estimates the effect before stopping study medicine. Here are Lilly's reported estimates for Zepbound 15 mg against Wegovy HD at week 72:
| Analysis | Difference in body-weight change | 95% credible interval |
|---|---|---|
| Treatment regimen | −4.5 percentage points | −6.3 to −2.8 |
| Efficacy | −1.8 percentage points | −3.8 to 0.1 |
A credible interval is the range where the model places 95% probability for the difference, given its assumptions. Negative numbers here favor Zepbound. The second range crosses zero, so no difference remains possible; that result did not reach statistical significance.
The headline gap therefore depends on which treatment question is asked. It isn't a promise of extra weight loss for someone switching medicines.
What Novo's heart-risk headline measured
COMPETE SWITCH CV was a real-world claims analysis, a study looking back through insurance billing records. It examined adults with type 2 diabetes already receiving Ozempic 1 mg, rather than people starting Wegovy HD for obesity.
The wider population numbered 636,525. The heart-outcome comparison included 185,705 people increasing Ozempic to 2 mg and 23,104 switching to Mounjaro. The measured outcome combined death from any cause, heart attack and stroke, called major adverse cardiovascular events, or MACE.
Novo described increasing Ozempic as associated with 6% lower relative risk. A hazard ratio compares event rates over time. After accounting for measured differences, it was 1.06 for switching versus increasing Ozempic, with a 95% confidence interval of 1.04–1.08. A confidence interval describes the estimate's statistical uncertainty.
That isn't six fewer events per 100 people. The release did not assess safety outcomes. It also acknowledges that unmeasured differences could affect the result.
Most importantly for this comparison, neither arm used Wegovy HD. The study cannot rank Zepbound against semaglutide 7.2 mg for heart protection.
What these announcements do not establish
Both analyses were backed by the manufacturer whose medicine was favored. Neither was a randomized comparison between Zepbound and Wegovy HD. Their limitations matter even when the number of people is large.
The direct obesity trial, SURMOUNT-5 in the New England Journal of Medicine, 2025, compared tirzepatide 10 or 15 mg with semaglutide 1.7 or 2.4 mg. It did not test 7.2 mg. SURMOUNT-5 results explains that study and its limits.
Safety needs its own evidence. In STEP UP, published in The Lancet Diabetes & Endocrinology in 2025, stomach or bowel problems affected about seven in ten people receiving 7.2 mg: 70.8%. That compared with 61.2% at 2.4 mg and 42.8% on placebo. Altered skin sensations, called dysaesthesia, occurred in 22.9%, 6.0% and 0.5%, respectively.
Those figures compare semaglutide doses within STEP UP. They cannot show which drug causes fewer side effects when compared with tirzepatide in a different trial.
The doses also aren't conversion instructions. The Wegovy label, which reads “Revised: 6/2026,” describes 7.2 mg only after tolerating 2.4 mg and when further weight reduction is indicated. A prescriber sets the actual dose and any change between medicines; switching from semaglutide to tirzepatide covers that process.
Tirzepatide and semaglutide prescribed through Promise are dispensed by a licensed U.S. compounding pharmacy as compounded medications, which is different from an FDA-approved product: the formulations offered here are not FDA-approved. A compounded medication is prepared by a pharmacy for a prescription. The FDA explains that it does not verify these preparations' safety, effectiveness or quality before marketing. Brand trial results do not establish matching results for a compounded preparation.
A licensed provider may still prescribe a compounded formulation; that decision is between the patient and the doctor.
What to watch next
As of September 30, 2026, the day this article was written, an earlier ENDO abstract reported the same comparison, with a 4.51-point estimate. It was presented at the Endocrine Society meeting in June 2026. The September release isn't the first public account of that weight comparison.
What would add more confidence is a direct trial against 7.2 mg, with clear plans for handling treatment stops and comparing side effects. For the heart analysis, fuller methods would help explain how well the two treatment groups were matched.
For a prescribing conversation, the useful questions stay personal: the treatment goal, response so far, side effects and other medicines. At Promise, a licensed provider reviews every request, and not everyone qualifies.
