Most current guidance no longer says to stop. The October 2024 guidance from five societies, including the American Society of Anesthesiologists, says most patients should keep taking GLP-1 medication before elective surgery, with a liquid diet for the 24 hours beforehand for those at highest risk (ASA 2024), and UK guidance published in January 2025 also says to continue (Anaesthesia 2025). The reason the question exists is that tirzepatide and semaglutide slow stomach emptying, and food left in the stomach under anaesthesia can be inhaled. For any particular operation or scope, the decision belongs to the anaesthetist and surgeon doing it, and the one thing every source agrees on is that they need to be told.

Availability in Singapore. Both medicines are registered with Singapore's Health Sciences Authority, and their registered indications include weight management. Which medicine suits a particular person, if any does, is decided by the doctor who assesses them.

Why it matters for anaesthesia

Because these medicines slow the stomach.

Both United States labels carry the same warning: the medicine delays gastric emptying, and there have been rare reports after marketing of pulmonary aspiration in people having procedures under general anaesthesia or deep sedation who still had food in the stomach despite fasting as instructed (Mounjaro label, Wegovy label). The labels add that the data are not enough to say whether changing the fast or pausing the medicine reduces that risk, and tell patients to inform their healthcare providers before any planned procedure. The European product information for tirzepatide says the increased risk of residual stomach contents should be considered before such procedures (EU SmPC).

How big the risk is remains uncertain. A 2025 meta-analysis found the medicines were associated with food remaining in the stomach despite appropriate fasting, but not with more pulmonary aspiration, with the certainty of evidence rated low for both findings (Elkin 2025).

What the guidance says now

It changed in 2024, from "hold it for a week" to "most people continue".

In June 2023 the American Society of Anesthesiologists advised considering holding a weekly GLP-1 medicine for a week before elective procedures, and described the evidence behind that as limited to several case reports (ASA 2023). In October 2024 five societies — anaesthesia, gastroenterology, bariatric surgery, perioperative care of patients with obesity, and endoscopic surgery — published joint guidance that replaced it (ASA 2024):

  • Most people continue their GLP-1 medication before elective surgery.
  • Those at highest risk of gastrointestinal side effects, including people on higher doses, follow a liquid diet for 24 hours before the procedure.
  • Elective surgery waits if someone is in the escalation phase or has symptoms such as nausea, vomiting, abdominal pain or constipation, until those have settled.
  • The decision is shared between the anaesthetist, the surgeon and the prescribing team.

The UK consensus of January 2025 also says to continue, with a full risk assessment and anaesthetic techniques that reduce aspiration risk (Anaesthesia 2025). The Australian and New Zealand recommendations of April 2025 go furthest on diet: they do not recommend stopping, and they recommend a 24-hour clear fluid diet followed by the standard six-hour fast for everyone taking these medicines, noting that feeling well is not a reliable sign that the stomach has emptied (ANZCA 2025).

What about a colonoscopy or gastroscopy?

The same reasoning applies to procedures under sedation, and the Australian and New Zealand recommendations are written for procedures generally, endoscopy included (ANZCA 2025). Bowel preparation for a colonoscopy already involves a clear fluid diet, which is one reason the instructions for a scope can differ from those for an operation. The unit doing the procedure sets them.

In Singapore

In October 2026 we searched for Singapore-specific guidance on this from the College of Anaesthesiologists, the Academy of Medicine, the Ministry of Health, the public hospitals and the Singapore Medical Journal, and found none. The guidance above is international, and a Singapore anaesthetist will apply their own judgement and their hospital's protocol.

What can be said for anyone with a procedure booked: the labels instruct patients to tell their healthcare providers, before any planned surgery or procedure, that they are taking the medicine (Mounjaro label). Do not stop or change the dose on your own; any change is agreed with the doctor who prescribed it and the team doing the procedure.

At GetLean, a patient with a procedure coming up can raise it with the care team on WhatsApp, and any change to the dose is Dr Quek's decision. The programme is designed to end, but an operation is not the moment to improvise an exit.

Common questions

Do you need to stop Mounjaro or Wegovy before surgery?

Most current guidance says no. The October 2024 guidance from five societies, including the American Society of Anesthesiologists, says most patients should continue before elective surgery, with a 24-hour liquid diet for those at highest risk (ASA 2024), and UK guidance from January 2025 also says to continue (Anaesthesia 2025). The anaesthetist and surgeon decide for a particular operation.

Why did people used to stop it a week before?

The American Society of Anesthesiologists advised that in June 2023, on evidence it described as limited to several case reports. In October 2024 it affirmed newer multi-society guidance that most patients should continue (ASA 2023).

Does it matter for a colonoscopy or gastroscopy?

The guidance covers procedures under sedation as well as surgery. The Australian and New Zealand recommendations of April 2025 advise a 24-hour clear fluid diet followed by standard fasting for everyone taking these medicines before a procedure (ANZCA 2025). The team doing the procedure sets the instructions.

Why do these medicines matter for anaesthesia?

They slow stomach emptying, so food can still be in the stomach after the usual fast. The labels warn of rare reports of pulmonary aspiration under general anaesthesia or deep sedation (Mounjaro label). A 2025 meta-analysis linked the medicines to leftover stomach contents but not to more aspiration, at low certainty of evidence (Elkin 2025).