GLP-1s and surgery: why fasting instructions may not be enough

Semaglutide. Tirzepatide. Liraglutide. These are now common medications in general practice — prescribed for type 2 diabetes, for weight management, for the metabolic overlap between both. And if a patient on one of them is heading to theatre, standard preoperative fasting may no longer be sufficient protection.

Australian anaesthetists are warning that the pharmacology of GLP-1 receptor agonists creates a perioperative safety gap that routine nil-by-mouth instructions do not address. The mechanism has been documented since these drugs were introduced — delayed gastric emptying is part of what makes them effective — but the warning is arriving now in the context of a patient population that is large, growing, and moving through surgical waiting lists.

The problem, in brief: GLP-1 agonists slow how quickly the stomach empties. That delay, which produces satiety and glycaemic benefit, means a patient who followed standard fasting instructions to the letter may still have significant residual gastric content at induction. Under general anaesthesia, with protective airway reflexes suppressed, that content can be aspirated into the lungs.

The scale of the gap

The concern is partly a function of how many patients are now on these medications. An estimated one in ten Australian adults has type 2 diabetes, and the proportion using injectable GLP-1 therapy is no longer marginal. Add the weight management prescriptions — Ozempic use beyond PBS-listed indications, private-market tirzepatide, Saxenda — and the patient pool taking weekly or daily GLP-1 injections in Australia is substantial.

Each of those patients, at some point, will need a procedure. Elective surgery, colonoscopy, cardiac catheterisation, dental work under sedation, laparoscopic gynaecological work. The fasting protocol they receive from the booking coordinator will, in most cases, not mention their GLP-1.

That is the gap the Australian Society of Anaesthetists and ANZCA have been working to close. ANZCA guidance issued in 2024 recommends withholding weekly GLP-1 formulations — semaglutide (Ozempic, Wegovy), dulaglutide (Trulicity) — for 7 days before elective procedures. Daily formulations — liraglutide (Saxenda, Victoza) — for at least 24 hours. That guidance has not reached every surgical booking form. It has not been communicated to every patient who hands over a medication list at pre-admission.

Both-and: effective medications with a pharmacological consequence

The tension here is not about whether GLP-1s are beneficial medications. They are. The trial evidence for glycaemic control, weight management, and now cardiovascular risk reduction is substantive. Many patients on these drugs have better metabolic outcomes than they had on any prior regimen.

And the gastric emptying delay is also real, and the aspiration risk is real, and the perioperative guideline infrastructure has been working to catch up with a class of medications that became widely prescribed faster than the surgical pre-assessment systems adapted.

The both-and framing: these drugs work, this effect matters under anaesthesia, and the required response is a conversation — not medication cessation or avoidance of necessary surgery. A patient stopping weekly semaglutide 7 days before an elective procedure is managing their medication safely, not abandoning it.

One note on urgency: for emergency or time-sensitive surgery, withholding a weekly GLP-1 is often not an option. In those cases, the anaesthetic team should be informed so they can apply appropriate airway management strategies. The conversation is still relevant — the approach is different.

2 cents

The GP is often the last clinical contact who can catch this before a procedure goes ahead.

When a patient mentions an upcoming surgery, colonoscopy, or any procedure requiring anaesthesia or sedation, the GLP-1 question is worth naming directly: “Are you on Ozempic, Wegovy, Mounjaro, or any other weekly injection for diabetes or weight management?” If yes: “The current anaesthetic recommendation is to stop it seven days before general anaesthesia — I want to flag that to your surgical team, because it doesn’t always get captured on the standard booking form.”

That conversation takes thirty seconds. A pulmonary aspiration event under GA is serious and potentially life-threatening. The population on these medications is large and still growing. The intervention — naming the medication, naming the withholding window, ensuring the anaesthetic team has the information — is genuinely low-cost and within every GP’s scope.

The practical audit question for this week: do patients on weekly GLP-1s who are awaiting elective procedures know to hold for seven days beforehand? If the referral went through without that discussion, a brief message to the patient — and a note to the referring or receiving team — takes five minutes and closes a real safety gap.

Verdict: yes — raise this with any patient on a GLP-1 agonist awaiting elective surgery or sedated procedure.

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Sources cited

1. GLP-1 research triggers surgery warning — The Medical Republic
2. About diabetes — Diabetes Australia