Using a GLP-1 medication in the run-up to surgery is now common practice in many programs, and for some patients it is the difference between being operable and not.
Why programs do it
Losing weight before surgery reduces liver size and visceral fat, which makes the operation technically easier and safer. That is the same reason for the pre-op diet, but medication can achieve considerably more than diet alone in patients who have the furthest to go.
Research presented at the ASMBS 2024 Annual Scientific Meeting looked at 113 patients with a BMI above 70, treated for an average of about 73 days. The results split clearly by approach:
- Multiple anti-obesity medications: 13.1 percent total body weight loss
- A single GLP-1: 8.14 percent
- Diet and exercise alone: 5.95 percent
The researchers noted this may help patients with extreme obesity lower their risk of post-operative complications, while being clear that more study is needed to establish the optimal role. Treat this as promising rather than settled.
Surgery after medication
A larger study, reported in May 2026 and drawn from the Epic Cosmos database covering 2019 to 2025, looked at more than 6,700 patients who took a GLP-1 within six months before surgery: 2,395 gastric bypass and 4,315 sleeve gastrectomy. They were compared against nearly 40,000 bypass and more than 87,000 sleeve patients with no prior GLP-1 use.
Those on medication beforehand lost around 8 percent of body weight pre-operatively, then went on to total weight loss of more than 25 percent after bypass and around 20 percent after sleeve. Patients who went straight to surgery lost only 2 to 3 percent more post-operatively than the GLP-1 group did. The practical reading is that prior GLP-1 treatment does not blunt what surgery achieves, and the pre-operative loss adds to the final result. The work was led by Dr Karan R. Chhabra at NYU Grossman School of Medicine.
What this means practically
If your BMI is very high, or your program has told you that you need to lose weight before they will operate, medication is worth raising specifically. Some insurers require a documented period of supervised weight loss before approving surgery, and medication may fit inside that requirement.
Questions to settle before you start
- Who is prescribing and who is monitoring? If the medication comes from a different provider than your surgeon, make sure both know.
- Does this affect your insurance approval for surgery? Some plans require a demonstrated failure of medical management before approving surgery; others treat medication as a substitute and may deny surgery while you are on it. Get this answered in writing.
- What happens to the medication around the operation? This is a genuine safety issue with specific guidance, and it is covered in GLP-1 Medications and Anesthesia. Do not assume you should simply stop.
- What is the plan afterwards? Whether you continue post-operatively, and for how long, should be decided deliberately rather than by default.
The thing to avoid
Starting a GLP-1 from an online provider without telling your surgical team, then arriving for surgery without anyone knowing, is the scenario the perioperative guidance exists to prevent. Your anesthesiologist needs this information. It changes what they do.