GLP-1 and Surgery Complications: USMLE Review of New Data

A large analysis of more than 2 million U.S. adults who had surgery found that people taking GLP-1 medications had fewer major cardiovascular complications and fewer infections afterward than similar patients who were not taking them. The results were presented at the ANESTHESIOLOGY 2026 annual meeting. The authors stress that this is an association, not proof that the drugs prevent complications.

What happened

Researchers led by Josephine Tolan, M.D., an anesthesiologist at McGovern Medical School at UTHealth Houston, used the Epic Cosmos database. It is a de-identified electronic health record database covering more than 1,700 hospitals and 40,000 clinics.

The study included adults 18 and older in the U.S. who had elective surgery lasting longer than 60 minutes and stayed in the hospital at least 24 hours afterward. The surgeries took place between January 2016 and December 2024.

Of 2,028,601 patients, 145,610 (about 7%) were taking GLP-1 medications. The investigators matched GLP-1 users with similar patients who were not taking them. After matching, GLP-1 use was associated with:

• 11% lower odds of major cardiovascular complications, defined as heart attack, heart injury, stroke or death.
• 8% lower odds of postoperative infections, including surgical site infections, urinary tract infections, pneumonia and sepsis.

Why it matters

GLP-1 receptor agonists are now part of everyday care for many people with diabetes or obesity. As Dr. Tolan noted, physicians still need more evidence on how these drugs behave around the time of surgery. Earlier research has shown that GLP-1 medications can lower the risk of heart-related problems in some patients. Their effect during and after surgery is less clear.

Surgery stresses the body. It can trigger inflammation and change blood pressure, blood sugar and circulation, all of which can influence the risk of cardiac complications and infection.

The authors offer possible explanations for the findings. These are hypotheses, not results of this study:

• Cardiovascular: weight loss, better blood pressure and glucose control, less inflammation, and possible protection of heart muscle during stress.
• Infection: better glucose control, since high blood sugar can weaken the immune response and make infections harder to fight.

Dr. Tolan called the results "encouraging" but said more research is needed to determine whether the medications themselves drive the benefit and how best to manage them before and after surgery.

What to know for the USMLE

This news is a good excuse to review GLP-1 pharmacology and the biostatistics of observational studies. Both show up on Step 1 and Step 2 CK.

• Physiology: GLP-1 is an incretin hormone secreted by intestinal L cells after a meal. The incretin effect is the greater insulin response to oral glucose than to the same glucose given intravenously. GIP, from K cells, is the other major incretin.
• Mechanism of GLP-1 receptor agonists: they increase glucose-dependent insulin secretion, decrease glucagon, slow gastric emptying, and promote satiety through central pathways. Because insulin release depends on glucose, hypoglycemia is uncommon when they are used alone.
• Drugs: semaglutide, liraglutide, dulaglutide and exenatide. Tirzepatide is a dual GIP/GLP-1 agonist.
• DPP-4 inhibitors (e.g., sitagliptin) work on the same axis by blocking the enzyme that degrades endogenous GLP-1.
• Adverse effects: nausea, vomiting and diarrhea are the most common. Also know acute pancreatitis and gallbladder disease (cholelithiasis). There is a boxed warning for thyroid C-cell tumors, and these drugs are contraindicated with a personal or family history of medullary thyroid carcinoma or MEN2.
• Anesthesia link: delayed gastric emptying is why these drugs come up in perioperative discussions. Retained gastric contents raise the theoretical concern of aspiration during anesthesia. The news source does not report on this, so treat it as background knowledge only.
• Why hyperglycemia raises infection risk: high glucose impairs neutrophil function (chemotaxis, phagocytosis, killing) and impairs wound healing. This is the textbook basis for the authors' glucose-control hypothesis.
• "Heart injury" after surgery: this likely refers to myocardial injury detected by troponin elevation, which can occur after noncardiac surgery even without chest pain. The source does not say how the study defined it.
• Biostatistics: this is a retrospective observational cohort using matching. Matching reduces measured confounding but cannot remove unmeasured confounding. Watch for confounding by indication and healthy-user bias. Only randomized controlled trials establish causation.
• Odds ratio vs. risk: "11% lower odds" describes an odds ratio of roughly 0.89. It is not the same as an 11% absolute reduction in risk.

Limitations

The authors say plainly that the study does not prove cause and effect. They analyzed existing medical records instead of randomly assigning patients to take or not take GLP-1 drugs, so other factors may have contributed to the lower complication rates.

Several points are worth keeping in mind when reading the numbers:

• Observational design. Even with matching, patients who receive GLP-1 drugs may differ from those who don't in ways the database doesn't capture. Examples include access to care, health behaviors or how closely they are followed.
• Conference presentation. The source describes results presented at a meeting. It does not mention peer-reviewed publication, so details may change as the work is reviewed.
• Missing details. The source does not say which GLP-1 drugs were used, at what dose, for how long, or whether patients were using them for diabetes or obesity. It also gives no absolute event rates and does not break out results by type of surgery.
• Limited scope. The cohort included only elective surgeries longer than 60 minutes with a hospital stay of at least 24 hours. The findings may not apply to emergency, brief or outpatient procedures.
• Management questions remain open. The authors note that more work is needed on how best to manage these medications before and after surgery. This study does not answer that question, and nothing here is a recommendation for any individual patient.

FAQ

Do GLP-1 drugs prevent complications after surgery?

This study cannot say. It found that GLP-1 use was associated with 11% lower odds of major cardiovascular complications and 8% lower odds of infections. Because it was observational, the authors say additional studies are needed to see whether the drugs directly reduce surgical complications.

What is the mechanism of action of GLP-1 receptor agonists for the USMLE?

They mimic the incretin GLP-1. They increase glucose-dependent insulin secretion, decrease glucagon, slow gastric emptying and increase satiety. Know the key adverse effects: GI symptoms, pancreatitis, gallbladder disease and the thyroid C-cell tumor warning (MEN2 and medullary thyroid carcinoma contraindication).

Why can't an observational study prove that a drug works?

Without randomization, the treated and untreated groups may differ in factors that affect the outcome. Matching only balances the characteristics that were measured. Hidden confounders can still produce an apparent benefit, so a randomized trial is needed to establish causation.

Key takeaways

• In more than 2 million surgical patients, GLP-1 use was associated with 11% lower odds of major cardiovascular complications and 8% lower odds of postoperative infections after matching. The study was observational and the authors say it does not prove causality.
• For the USMLE, know that GLP-1 agonists are incretin mimetics: they increase insulin, decrease glucagon, slow gastric emptying and promote satiety. Know their adverse effects and contraindications.
• Use this study to practice critical appraisal: matching does not eliminate confounding, and an odds ratio is not an absolute risk reduction.