Why You Must Tell Your Surgeon About GLP-1s + Peptides

Don't ever lie to your surgeon about what you're doing.

If you're getting ready for surgery, it's very important that you're transparent with your surgeon about what peptides you're taking, especially GLP-1s.

And to understand why that matters so much, you have to see the whole chain, from the injection you gave yourself last Sunday all the way to the moment the anesthesiologist puts you under, because every step in that chain assumes something about your body that a GLP-1 quietly changes.

The chain runs like this: you stop eating the night before, your stomach empties on a predictable schedule, you arrive with an empty stomach, the anesthesiologist gives you drugs that relax every muscle you have including the ring of muscle at the bottom of your esophagus, your gag reflex and cough reflex switch off, and for the next few hours the only thing keeping stomach contents out of your lungs is the fact that there aren't any stomach contents.

Break the first link and the last one becomes a problem.

The fasting rules you get handed before surgery, no solid food for six to eight hours and clear liquids up to two hours, were built from studies on stomachs that empty normally. They aren't arbitrary numbers someone picked out of the air, but a measurement of how long a typical stomach takes to clear itself, with a safety margin built in.

GLP-1 receptor agonists work partly by extending that clearance time on purpose. When semaglutide or tirzepatide binds the GLP-1 receptor, one of the downstream effects is slowed gastric emptying through vagal signaling, so food sits in the stomach longer, so you feel full longer, so you eat less. The delay is not a side effect that came along for the ride. It is part of the mechanism you paid for.

Which means the fasting window that empties a normal stomach may not empty yours.

That stopped being theoretical when Sen and colleagues published a study in JAMA Surgery in 2024 where they used gastric ultrasound to look inside the stomachs of 124 patients who had all followed standard preoperative fasting instructions, and they compared GLP-1 users to matched nonusers. Increased residual gastric content showed up in 56 percent of the GLP-1 users compared to 19 percent of the people not taking one, which came out to an adjusted prevalence ratio of about 2.5.

These patients had done everything they were told, fasting on schedule and following the instructions printed on their paperwork, and more than half of them still had food or thick fluid sitting in their stomach when they were wheeled in.

The obvious question is how long you have to be off the drug for that to stop being true, and the answer depends on which drug you're on, because the pharmacology varies enormously across the class.

Milder and colleagues laid this out in a narrative review in Anaesthesia in 2024. Semaglutide has an elimination half-life around one week, tirzepatide sits around five days, liraglutide is roughly thirteen hours, and the older short-acting agents clear in a matter of hours. Five half-lives is the usual rule of thumb for getting a drug functionally out of the system, and for semaglutide that arithmetic lands you at something like five weeks, not five days.

I know that for people on Ozempic, because of the things that it's doing with your body, they're actually asking that you come off of that stuff for at least, I think, four to eight weeks before you actually go into surgery.

That range is wider than what some of the official guidance says, and it's worth understanding why the guidance itself has been moving. The American Society of Anesthesiologists put out advice in 2023 suggesting a one week hold for weekly injectables, and van Zuylen and colleagues pushed back in the British Journal of Anaesthesia in 2024, pointing out that a one week hold on a drug with a one week half-life still leaves you with roughly half the drug on board, and that gastric emptying effects have been documented well past that window.

More recent multisociety guidance has moved away from a single number entirely and toward risk stratification, which is what Goldenberg and colleagues built into the STOP-GAP algorithm published in Current Medical Research and Opinion in 2025. The logic there is that a patient on a low maintenance dose with no nausea, no vomiting, and no reflux is in a very different situation from someone who just escalated their dose two weeks ago and is still feeling it, and the recommendation should reflect that instead of applying one rule to everybody.

Palmer and colleagues looked at anesthesia-related complications before total joint replacement in patients using GLP-1 receptor agonists and published in the European Journal of Orthopaedic Surgery and Traumatology in 2025, finding that the rate of actual complications was low, which tells you aspiration isn't common even if it isn't zero. That finding is real and you should weigh it.

But low probability and low consequence are not the same thing. Aspiration of stomach acid into the lungs during induction can produce a chemical pneumonitis that turns a same-day procedure into an intensive care admission, and in the worst cases it kills people. When the downside is that shaped, you manage the tail, not the average.

There's a second layer to this that has nothing to do with your stomach.

GLP-1s change how your body handles glucose, and if you're diabetic and taking one alongside insulin or other agents, stopping abruptly for a month without adjusting the rest of your regimen can send your blood sugar in the other direction. Surgery itself raises cortisol and drives insulin resistance, so you're stacking a stress response on top of a medication change. That's a conversation for your prescribing physician, not something to figure out on your own the week before.

And if you've lost a significant amount of weight on a GLP-1, your anesthesiologist is calculating drug doses based on body composition, because as Arora and colleagues discussed in Current Opinion in Anaesthesiology in 2024, obesity changes airway management, changes how lipophilic anesthetics distribute into fat tissue, and changes how long you take to wake up. Someone who was 280 pounds nine months ago and is 205 pounds now, with an unknown amount of that loss coming from lean mass, is a different pharmacological problem than either of those numbers alone suggests.

Everything above applies specifically to GLP-1s because that's where the research is. The rest of the peptide world is a different situation, and it's worth being straight about the evidence.

BPC-157 and TB-500 are used for tissue repair, and both are described as promoting angiogenesis, the growth of new blood vessels. Whether that meaningfully changes bleeding, clotting, or healing during a surgical procedure in a human being has not been studied in any way I'd call conclusive, mostly because the human data barely exists, and past that gap, nobody actually has an answer.

Growth hormone secretagogues like ipamorelin and CJC-1295 raise IGF-1 and can push insulin resistance and fluid retention, both of which show up in perioperative management, and the specific surgical evidence for these compounds stays just as sparse.

Thin evidence is the argument for disclosure, not against it. Your surgeon and your anesthesiologist can only account for what they know about, and a compound with unclear effects that they've been told about is a manageable unknown, while the same compound they haven't been told about is a surprise in the middle of a procedure.

Put the practical version on paper: write down every peptide, hormone, and supplement you're taking, with the dose and the date of your last injection, and hand that list over at your pre-op appointment, not on the morning of surgery. Weeks of notice gives your team room to adjust the plan. An hour of notice gives them room to cancel.

My advice to you is if you are doing surgery, you wanna minimize the number of variables, which is why it's very important that you come off of everything, you know, like I said, four weeks before, especially if you're going under.

Plan for what that hold feels like, because it isn't nothing. Appetite comes back, and for a lot of people it comes back hard, and four to eight weeks is enough time to regain a meaningful amount of weight if you go into it without a plan. Keep protein high, keep resistance training in place so you're protecting lean mass going into a period where you'll be immobilized afterward, and if you're diabetic, monitor glucose more closely than usual during the transition.

If your surgery is urgent and there's no time for a proper hold, say so anyway, because there are tools for that. Gastric ultrasound at the bedside can show whether there's residual content before induction, a 24 hour clear liquid diet can reduce what's sitting there, and rapid sequence induction with cricoid pressure changes how the airway is secured. All of those options require your team to know.

And the last thing that we want is for there to be an unaccounted for variable that could potentially impact the way that your surgeon does the surgery, or even worse, your anesthesiologist manages your care while you're under.

Most people who hide this stuff hide it out of embarrassment, because they don't want to explain where they got it or why they're taking it, and they assume the doctor will lecture them. Your anesthesiologist isn't grading you on any of it, only building a prediction of how your body will respond to being shut down and restarted, and every drug you leave off the list is a variable removed from that prediction, which is the one thing that makes the whole procedure safe.

References:

Arora L, Sharma S, Carillo JF. Obesity and anesthesia. Curr Opin Anaesthesiol. 2024. https://pubmed.ncbi.nlm.nih.gov/38573180/

Milder DA, Milder TY, Liang SS et al.. Glucagon-like peptide-1 receptor agonists: a narrative review of clinical pharmacology and implications for peri-operative practice. Anaesthesia. 2024. https://pubmed.ncbi.nlm.nih.gov/38740566/

C Palmer R, Telang SS, Kistler NM et al.. GLP-1 receptor agonist utilization is associated with a low risk of Anesthesia-related complications prior to total joint arthroplasty. Eur J Orthop Surg Traumatol. 2025. https://pubmed.ncbi.nlm.nih.gov/41351714/

Sen S, Potnuru PP, Hernandez N et al.. Glucagon-Like Peptide-1 Receptor Agonist Use and Residual Gastric Content Before Anesthesia. JAMA Surg. 2024. https://pubmed.ncbi.nlm.nih.gov/38446466/

Goldenberg RM, Gilbert JD, Houlden RL et al.. Perioperative and periprocedural management of GLP-1 receptor-based agonists and SGLT2 inhibitors: narrative review and the STOP-GAP and STOP DKA-2 algorithms. Curr Med Res Opin. 2025. https://pubmed.ncbi.nlm.nih.gov/39871617/

van Zuylen ML, Siegelaar SE, Plummer MP et al.. Perioperative management of long-acting glucagon-like peptide-1 (GLP-1) receptor agonists: concerns for delayed gastric emptying and pulmonary aspiration. Br J Anaesth. 2024. https://pubmed.ncbi.nlm.nih.gov/38290907/