Preoperative GLP-1 Use Doesn't Change Bariatric Weight Loss Outcomes

As glucagon-like peptide-1 receptor agonists (GLP-1 RAs) become a common first stop in obesity treatment, a growing share of patients arrive at bariatric surgery already taking one, raising the question of whether prior exposure helps or blunts surgical results.

A research letter published in JAMA Surgery offers an early answer: Preoperative GLP-1 RA use was not associated with any significant difference in weight loss 12 months after surgery. For pharmacists counseling patients through the transition, it's a reassuring but nuanced data point.^1,2

What the Study Looked At

Investigators retrospectively reviewed all patients who underwent primary bariatric surgery from 2022 to 2024 at a single center. Of 383 patients, 92 (24%) were taking a GLP-1 RA preoperatively; semaglutide (Ozempic, Wegovy; Novo Nordisk) was the most common agent, and most patients were not at the maximum dose.

Patients taking a GLP-1 RA were broadly similar to those who were not, though diabetes was more prevalent (51% versus 16%; P < .001) and mean hemoglobin A1c was higher. The primary outcome was total body weight loss percentage (TWL%) at 12 months, with 88% follow-up.¹

No Difference in Weight Loss

At 12 months, there was no significant difference in TWL% between patients who did and did not use a GLP-1 RA preoperatively (mean, 24% vs 25%; P = .33) and no difference in excess weight loss (60% vs 62%; P = .65). A multivariate regression confirmed that preoperative GLP-1 RA use was not a predictor of TWL% after adjustment. Instead, higher baseline BMI and male sex were independently associated with greater 12-month TWL%, while diabetes and sleeve gastrectomy were associated with lower TWL%. There were no significant differences between groups in operative time, length of stay, 30-day emergency department visits, or complications.¹

Corresponding author Jonathan Carter, MD, professor of clinical surgery at the University of California, San Francisco, said the neutral headline finding shouldn't be read as GLP-1 RAs adding nothing. While his team could not measure GLP-1–induced weight loss before surgery, he pointed to a yet-to-be-published study presented at the American Society for Metabolic and Bariatric Surgery 2026 annual meeting that found patients lost roughly 8% of their total body weight on GLP-1 RAs before surgery.³

"In that study, patients who were on GLP-1s going into surgery did lose about 2% to 3% less weight than GLP-1-naive patients who had surgery," Carter said, "but when you consider the 8% TWL head start that the GLP-1 patients enjoyed, the combination of GLP-1 plus surgery had far better weight loss than surgery alone." The practical takeaway for counseling: a patient's pre-surgical losses appear to carry forward, even if the surgery itself delivers slightly less on top.¹

Diabetes Control and Restarting Therapy

Diabetes control was strong in both groups at 12 months, with a mean hemoglobin A1c (HbA1c) of 5.4% in the GLP-1 RA group and 5.3% in the comparison group (P = .44). Although the study team recommended discontinuing GLP-1 RAs after surgery to prevent vomiting, 15 patients resumed therapy—5 for diabetes management, 8 for weight control, and 2 for unknown reasons. Their 12-month TWL% was statistically similar to that of patients not taking a GLP-1 RA.¹

Carter noted that the study's caution against restarting therapy in the first year reflected a concern that has since eased. "We discouraged GLP-1 reinitiation in the first year because we were worried about undue nausea and vomiting from the recent surgery added to GLP-1," he said. "But evidence is evolving, and recent studies have shown it is safe to resume GLP-1s much earlier."

He added that he would now have no problem reinitiating GLP-1 therapy 6 to 8 weeks after surgery.¹

An Important Caveat on Interpretation

The neutral finding comes with a limitation the authors underscore: the study could not quantify how much weight patients lost on a GLP-1 RA before surgery. They contrast their result with earlier work by Mathur and colleagues, in which patients who had already lost weight on preoperative semaglutide went on to lose less after surgery, such that both groups converged at similar total weight loss by 12 months. The authors also could not determine duration of therapy before surgery or break results out by procedure type, and they call for further research on the optimal sequencing of GLP-1 RAs and bariatric surgery.^1,4

REFERENCES

1. Huynh RL, Prosser R, Manasa M, et al. Preoperative GLP-1 receptor agonist use and weight loss outcomes after bariatric surgery. JAMA Surg. Published online August 12, 2026. doi:10.1001/jamasurg.2026.3327

2. Preoperative GLP-1 receptor agonist use and weight loss outcomes after bariatric surgery. News release. JAMA Network; August 12, 2026. Accessed August 26, 2026. https://www.eurekalert.org/news-releases/1139575

3. New study finds metabolic and bariatric surgery after GLP-1 treatment significantly boosts weight loss. News release. American Society for Metabolic and Bariatric Surgery. Released May 5, 2026. Accessed September 1, 2026. https://asmbs.org/news_releases/new-study-finds-metabolic-and-bariatric-surgery-after-glp-1-treatment-significantly-boosts-weight-loss/

4. Mathur V, Wasden, Shin TH, et al. Neoadjuvant semaglutide, bariatric surgery weight loss, and overall outcomes. JAMA Surgery. 2025;160(5):594-596. doi:10.1001/jamasurg.2025.0001