GLP-1s, Surgery, and Procedures

If you take one thing from this page: tell them, out loud, without being asked. Everything else is detail that other people will manage for you.

What the actual risk is

General anaesthesia suppresses the reflexes that normally keep stomach contents out of your airway. Preoperative fasting rules exist to make sure there is nothing in the stomach at that moment, and those rules were written assuming a stomach that empties at a normal rate.

These drugs slow gastric emptying — that is part of how they work — so food and fluid can still be present after a standard overnight fast, even in someone who followed the instructions to the letter. Anaesthetists have reported finding solid food in stomachs that should have been empty.

The consequence is aspiration: stomach contents entering the lungs. It is uncommon and it is serious, which is exactly the risk profile that justifies preparation rather than panic.

This is a preparation and timing problem, not a reason to avoid necessary surgery.

What the guidance says now

The first widely publicised advice, from the American Society of Anesthesiologists in 2023, suggested holding these drugs before elective procedures — 1 day for daily agents, 1 week for weekly ones.

That advice has since been refined. A 2024 multisociety guidance, developed jointly across anaesthesia, surgery, gastroenterology and obesity medicine, moved towards risk stratification rather than blanket withholding, for a sound reason: stopping the drug has costs of its own, including loss of glycemic control in people with diabetes, and the pharmacology means a one-week hold does not do what people assumed it did.

What that looks like in practice varies by centre, and commonly includes some combination of:

• A clear-liquid diet for 24 hours before the procedure, which addresses the actual problem more directly than skipping a dose
• An extended fasting period beyond the standard
• Gastric ultrasound on the day, where available, to assess directly whether the stomach is empty
• Treating you as a full stomach anaesthetically, with the airway technique that implies
• Sometimes holding a dose, as part of a plan rather than as the plan

Your centre’s protocol governs. Ask them, and ask early.

Why holding one dose is not clearance

This is the misconception worth correcting, because it produces false reassurance on both sides.

Semaglutide and tirzepatide both have a half-life of roughly a week. Skip one weekly dose and about half the previous concentration remains; substantial clearance takes 4–5 weeks. A person who skipped last Sunday’s injection is not “off” the drug in any meaningful sense, and the delayed emptying does not switch off because a dose was missed. The arithmetic is in how long these drugs stay in your system.

So a hold may be a sensible part of a plan. It is not a substitute for the team knowing, and it should never be used to avoid mentioning it.

Endoscopy has a second problem

For upper endoscopy specifically, there is a practical issue on top of the safety one: retained food obscures the view. The endoscopist cannot see the mucosa they were sent to look at, so the procedure is abandoned and rebooked — costing you the preparation, the sedation, and often 3–6 months of waiting.

Many units now specify a longer clear-liquid period before endoscopy in patients on these drugs. Tell them when you book, so they can plan the preparation, rather than on the day, when the options are to proceed suboptimally or cancel.

What to say, and when

The failure mode here is almost never clinical judgement. It is information not reaching the person who needed it.

Do not assume it is in your notes. Say it every time. It takes four seconds and it is the entire intervention.

Two additions worth mentioning alongside it: whether you have had symptoms suggesting the drug is delaying emptying more than usual — persistent vomiting, feeling full for hours after eating, vomiting undigested food — and whether you also take insulin or a sulfonylurea, which changes fasting management entirely.

Do not stop it on your own

If you decide unilaterally to stop the drug for a few weeks before an operation, two things follow. Glycemic control may drift if you have type 2 diabetes, which is its own perioperative risk. And restarting afterwards is not simply picking up where you left off — tolerance fades, and resuming a high dose after a gap can produce the side effects of a first injection at a dose several steps up the ladder, as covered in what to do if you miss a dose.

The stop-and-restart plan should come from the team, and it should include the restart, which people routinely forget to ask about.

Procedures this applies to

Anything with sedation or general anaesthesia, which is a longer list than people assume:

• Surgery of any kind, including day cases
• Upper endoscopy and colonoscopy
• Dental procedures under sedation or general anaesthesia
• Cardiac catheterisation, bronchoscopy, and similar
• Some imaging requiring sedation
• Obstetric anaesthesia, including planned caesarean section

If someone is going to sedate you, they need to know. This sits alongside the other red-flag disclosures in the side-effects piece, and it is the one most likely to be forgotten precisely because you feel fine.