Pulse ·

Semaglutide and surgery: the aspiration risk most patients aren't told

By Dr HB Lo, FACRRM 3 min read
Verdict Yes — worth knowing about

A UK cohort study confirms patients on GLP-1 receptor agonists — semaglutide, liraglutide, tirzepatide — face substantially elevated aspiration risk during general anaesthesia. The mechanism is delayed gastric emptying: these medicines slow the gut intentionally, and that slowing persists beyond standard fasting windows.

Anaesthetists are advising GLP-1 patients be treated as "potentially full stomach," and many centres now recommend holding the weekly injection for one cycle before elective procedures.

If you take a GLP-1 medicine and have surgery coming up, raise it explicitly with your GP and anaesthetic team — the fasting protocol may not account for it.

If you have started one of the new weight-loss injections — Ozempic, Mounjaro, Wegovy — and you have surgery planned, there is something your anaesthetist needs to know before they put you under. There is a reasonable chance no one has told you this yet, and no one has told the anaesthetist either.

A UK cohort study reported this week has found that patients on GLP-1 receptor agonists face substantially elevated aspiration risk during general anaesthesia compared with patients not on these medicines. The finding has been circulating in anaesthetic and peri-operative medicine circles for a couple of years as case reports and mechanistic reasoning. This UK cohort adds scale to what was already a serious enough concern. The signal is real and it is not going away.

What the study found

The mechanism is delayed gastric emptying.

One of the ways GLP-1 receptor agonists — semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro), liraglutide (Victoza, Saxenda) — achieve their therapeutic effects is by slowing the movement of food and liquid out of the stomach. This is intentional. You feel fuller longer. Appetite is suppressed. Blood glucose rises more gradually after meals. For the patient taking their weekly injection, this is the feature, not the bug.

Under general anaesthesia, it becomes a hazard.

Standard pre-operative fasting guidelines assume normal gastric emptying. The conventional rule — nothing to eat for at least 6 hours, clear fluids up to 2 hours before induction — is calibrated to this assumption. GLP-1 medicines extend the emptying window in ways that vary between patients, doses, and individual medicines, and they are not reliably accounted for by standard fasting intervals. The UK cohort found patients on GLP-1 RAs had substantially higher rates of aspiration events during anaesthetic induction: the inhalation of gastric contents into the airway when the patient’s protective reflexes are suppressed. Aspiration pneumonitis and pneumonia are major peri-operative complications that, in vulnerable patients, can be fatal.

The both-and

The counterpoint worth holding: GLP-1 receptor agonists are genuinely transformative medicines. The cardiovascular and metabolic evidence for semaglutide in particular — including the SELECT trial in people with cardiovascular disease and the STEP programme in obesity — is among the strongest in metabolic medicine in a decade. Many Australians are now on these medicines. The message from this finding is emphatically not stop taking them.

The message is: tell people before surgery.

There is also genuine debate within anaesthetic medicine about how to manage this. Some centres are recommending patients hold the weekly injection for one full cycle (7 days) before elective procedures. Others are using extended fasting protocols, treating GLP-1 patients as “potentially full stomach” regardless of stated fasting time and applying rapid-sequence induction. Neither approach has a settled universal evidence base. What the Australian and New Zealand College of Anaesthetists and similar bodies now agree on is that GLP-1 status needs to be documented, communicated, and actively managed before any procedure involving sedation or general anaesthesia.

The breakdown the UK study exposes is not in the medicine. It is in the information pathway. Patients are not thinking to mention their GLP-1 injections — they may not even think of Ozempic as a relevant surgical detail. GPs are not consistently documenting it in referral letters. Anaesthetists are not always asking.

What this means for you this week

If you are on any GLP-1 receptor agonist — semaglutide, tirzepatide, liraglutide, dulaglutide — and you have any surgical or procedural intervention coming up that involves sedation or general anaesthesia, raise it explicitly at your pre-operative assessment.

Tell the anaesthetic team:

  • The name of your medicine
  • Your current dose
  • When you last took it

If you have surgery booked and have not yet had a pre-op assessment, flag it with your GP now so it goes into the referral documentation. The question to ask is straightforward: “Does the fasting protocol account for the fact that I am on a GLP-1 medication?”

If the answer is a blank look or a simple “just follow the standard instructions,” that is a signal to push further — or to ask for the anaesthetic team to be briefed before you arrive.

This finding does not change the benefit profile of GLP-1 medicines. It validates the importance of careful pre-operative communication — which is not something the current system is reliably providing.

Verdict: yes — worth knowing about.

Sources cited

  1. Patients on GLP-1 receptor agonists at significantly higher aspiration risk under anaesthesia — AusDoc, 29 September 2026. https://www.ausdoc.com.au/news/patients-on-glp-1-receptor-agonists-at-significantly-higher-aspiration-risk-under-anaesthesia-uk-study-finds/

Frequently asked questions

  • Do I need to stop my semaglutide before surgery?

    This is evolving and depends on your medicine, dose, and type of procedure. Some anaesthetic centres recommend holding the weekly injection for one cycle (7 days) before elective general anaesthesia; others use extended fasting protocols. Do not stop the medicine without speaking to your GP first — and proactively raise this at your pre-operative assessment. Your anaesthetic team will decide the appropriate approach once they know your situation.

  • Why do GLP-1 medicines affect gastric emptying?

    GLP-1 receptor agonists work partly by mimicking the hormone glucagon-like peptide-1, which slows the movement of food out of the stomach. This is intentional — it extends satiety and blunts post-meal glucose spikes. But it also means the stomach empties more slowly than standard fasting calculations assume. Under general anaesthesia, residual gastric contents can be aspirated into the airway, causing aspiration pneumonitis or pneumonia — a serious peri-operative complication.

  • What should I tell my anaesthetist?

    Tell them the name of your GLP-1 medicine (for example Ozempic, Wegovy, Mounjaro, Victoza), your current dose, and when you last took it. Mention it at your pre-operative assessment and ask your GP to include it in the referral letter. The anaesthetic team will then decide on the appropriate fasting protocol and whether to recommend a temporary hold before the procedure.