Prior GLP‑1 users had fewer 90‑day heart and kidney events after bariatric surgery, in a design that cannot show cause

Adults who had filled a prescription for a GLP-1 medicine or tirzepatide in the year before metabolic and bariatric surgery had fewer serious heart and kidney problems in the first 90 days after the operation than closely matched patients who had not. The retrospective study was posted by The American Journal of Medicine on September 14, 2026.

The absolute numbers are small. Among 11,052 prior users, 36 had a major heart event within 90 days. Among 11,052 matched non-users, 67 did. That is 0.3% against 0.6%.

Two matched groups of 11,052 patients, split by a prescription fill

The researchers used a United States medical records database covering adults who had metabolic and bariatric surgery between 2016 and 2025. A patient counted as a prior user if there was at least one GLP-1 receptor agonist or tirzepatide prescription between 365 days and 7 days before the operation. Anyone with a prescription in the final week before surgery was excluded.

The authors then used propensity score matching. That is a statistical method that pairs each treated patient with an untreated patient who looks similar on characteristics the database recorded, such as age, body weight and other diagnoses. It produced two groups of 11,052 that the authors describe as well balanced at the start.

Serious heart events affected 36 prior users and 67 non-users

The main outcome was a measure researchers call four-point MACE, which bundles several serious cardiovascular events into one count so groups can be compared. Prior users had a hazard ratio of 0.535, with a 95% confidence interval running from 0.357 to 0.803.

A hazard ratio below 1 means the event happened less often in the group that had the exposure. The confidence interval is the range of values the data are reasonably consistent with. Here the whole range sits below 1, so within this dataset the difference is unlikely to be chance alone. That is a separate question from whether the medicine caused it.

Kidney events were the more common outcome, and the gap was narrower

Kidney problems in the first 90 days after surgery turned up more often than heart events: 158 prior users, or 1.4%, and 256 non-users, or 2.3%. The hazard ratio was 0.613, with a confidence interval from 0.502 to 0.747.

The authors also report lower rates of coronary events and heart failure among prior users. They do not give separate figures for those in the abstract.

Nobody was assigned to take a GLP-1, and that changes how to read this

This is an observational study, not a randomized trial. Patients ended up on a GLP-1 for reasons the database may not capture, and those reasons can track with health.

In the United States, being on one of these medicines before bariatric surgery usually means having coverage that paid for it, a prescriber who followed through, and enough tolerance of the side effects to keep refilling it. People who clear all three hurdles tend to differ from people who do not, in ways that matching on recorded variables does not fully correct. Researchers call this healthy user bias, and it pushes results in exactly the direction seen here.

The 7-day exclusion window is worth noting for a different reason. Patients who filled a prescription in the final week before surgery were deliberately removed from this analysis, so the study does not address what happens when one of these medicines is taken right up to the day of an operation. That timing question is handled by separate anesthesia guidance and is not what these numbers measure.

What the authors say their own result supports

The conclusion is measured. The authors write that the findings support further investigation of preoperative metabolic optimization and its potential role in improving postoperative cardiorenal outcomes. That is a call for more research, not a recommendation to start or continue a medicine before surgery.

Decisions about whether to take a GLP-1 before an operation, and when to stop it, belong with the surgical and prescribing team, who will weigh the anesthesia guidance alongside everything else.