ASMBS-presented Epic Cosmos data show people who took semaglutide or tirzepatide before bypass or sleeve still reached large total losses after the operation.
What happened
NYU Grossman School of Medicine researchers reviewed Epic Cosmos records from 2019 through 2025 for people prescribed a GLP-1 medicine in the six months before metabolic surgery. The medication-exposed group included 2,395 gastric bypass and 4,315 sleeve cases. Comparators without recent GLP-1 use numbered about 40k bypass and roughly 87k sleeve cases without recent medication.
People on semaglutide or tirzepatide lost roughly 8% of body weight in the months before the operation. After surgery, cumulative loss rose above 25% with bypass and about 20% with sleeve. Direct-to-surgery patients were only about 2 to 3 percentage points higher after the procedure, which the authors read as little loss of surgical effect after prior medication.
Restarting medication after surgery was common. In year one, about 44% of prior-GLP-1 bypass patients and 57% of sleeve patients resumed a drug. By year three, roughly two-thirds of the prior-medication group were back on a GLP-1. ASMBS President Richard Peterson, not on the study team, said medicines may open a journey that surgery still finishes for many people with severe obesity.
What it means
Someone already on a GLP-1 who is evaluating an operation can use this as evidence that recent medication exposure, by itself, was not linked to a large drop in one-year surgical weight outcomes in this dataset. Teams may still plan how long to hold a drug around anesthesia and how to handle restart decisions later.
High post-op restart rates also support treating obesity as chronic care rather than a one-and-done choice between a pen and an operation.
What it does not mean
It is not a promise of a specific percentage for any reader. It does not say every patient needs lifelong medication after surgery, or that medication before surgery is required. It is observational electronic-record work, not a randomized trial of sequencing.
Sources
Related guide
Bariatric surgery Information Center hub
Related discussion
GLP-1 Weight Loss Medications forum
Educational information only. Not medical advice. Do not start, stop, or change treatment from this brief.