US nationwide cohort of 208,155 post-bariatric patients finds tirzepatide outperforms semaglutide

People who regain weight after bariatric surgery are increasingly being prescribed GLP-1 and dual GIP/GLP-1 drugs. A new nationwide US cohort study published in eClinicalMedicine looked at how well that works in practice, and found tirzepatide was linked to substantially more weight loss than semaglutide after surgery ^[1][2].

Researchers used a de-identified electronic health record dataset drawn from 43,104 academic and private medical centers across the United States, covering 2018 to 2025 ^[2]. The analysis included 208,155 people who had metabolic and bariatric surgery (MBS). Of those, 39,750 received incretin-based therapy after their operation ^[2].

What the study found

Among patients who stayed on treatment for at least one year, tirzepatide (sold as Mounjaro and Zepbound) was associated with 17.2% total weight loss compared with 12.0% for semaglutide (Ozempic, Wegovy, Rybelsus) ^[2]. After statistical adjustment, the gap was 5.16 percentage points (95% confidence interval 4.17 to 6.16, p < 0.001), and the effect was dose-dependent for both drugs ^[2].

Timing also mattered. Among people who started therapy at least 12 months after surgery, those who began latest — between postoperative months 53 and 79 — had 15.4% total weight loss, compared with 13.5% for those starting in the first quartile, postoperative months 12 to 24 (p < 0.001) ^[2]. The study also compared results by surgical anatomy, sleeve gastrectomy versus Roux-en-Y gastric bypass, but the specific figures for that breakdown are not given in the abstract ^[2].

On heart outcomes, the picture was neutral. Using propensity-score matched groups and inverse probability of censoring-weighted Cox models, incretin therapy overall was not associated with a change in risk of major adverse cardiovascular events (MACE), defined as non-fatal heart attack, non-fatal stroke, or cardiovascular death (hazard ratio 0.91, 95% CI 0.80 to 1.05, p = 0.19) ^[2]. The pooled analysis matched 35,651 treated patients with 35,651 untreated patients and counted 884 MACE events — 377 among treated patients and 507 among non-users ^[2]. Separate matched comparisons included 22,797 semaglutide users and 12,854 tirzepatide users, each against equal numbers of non-users ^[2].

Why it matters for patients

Weight regain after bariatric surgery is common, and until now most evidence about adding a GLP-1 drug afterward has come from small single-center series. This study is much larger, and it is one of the first to put a number on the difference between the two most-used agents in a post-surgical population ^[2].

The results come with real limits. This was a retrospective study built from electronic health records, not a randomized trial. The authors themselves write that future prospective studies are needed to establish causality, to see how long the added weight loss lasts, and to determine whether these drugs add cardiovascular protection on top of surgery ^[2]. Results were also limited to people who stayed on therapy for a full year, so they do not describe what happens to patients who stop early — a group the abstract does not quantify ^[2].

The MACE finding is worth reading carefully. A hazard ratio of 0.91 with a confidence interval crossing 1.00 means the study could not show either benefit or harm to the heart over the follow-up period ^[2]. That is different from proving the drugs have no cardiovascular effect in this group; it means the question remains open in post-surgical patients specifically.

On timing, the finding that later initiation was linked to more weight loss is an association, not proof that waiting is better. People who start a drug years after surgery may differ in important ways from those who start at 12 months, and the study design cannot separate those factors ^[2].

Funding and disclosures

The study received no specific grant from public, commercial, or not-for-profit funders ^[2]. Among the authors, one serves on an advisory board and speaker's bureau for Eli Lilly, which makes tirzepatide, and on an advisory board for Boehringer Ingelheim; another is a speaker for Medtronic and advisory board member for Ethicon; a third consults for Intuitive Surgical and UBS. The remaining authors declared no competing interests ^[2].

Whether insurers or surgical programs change how they handle post-bariatric prescribing in response to these data is not addressed in the sources.