GLP-1 Medication Before Surgery and Anaesthesia

If you take Mounjaro (tirzepatide), Wegovy (semaglutide) or another GLP-1 medicine and have an operation, sedation or endoscopy planned, the most important step is to tell your surgical and anaesthetic team early. These medicines slow stomach emptying, which can raise the risk of stomach contents being inhaled under anaesthesia. Current UK multi-society guidance, published in 2025, generally advises continuing treatment rather than stopping it, with the team assessing and reducing risk instead. Your own team's instructions always come first.

Why GLP-1 medicines matter for anaesthesia

How they affect the stomach

GLP-1 receptor agonists mimic a natural gut hormone. One of their effects is to slow the rate at which food leaves the stomach. That contributes to the feeling of fullness that helps people eat less, and it is part of why nausea, bloating and reflux are common side effects. Tirzepatide, which acts on both GIP and GLP-1 receptors, has a similar effect. Our guide to what GLP-1 medications are explains the mechanism in plain English.

The aspiration concern

Before a general anaesthetic or deep sedation, patients are asked to fast. The reason is that anaesthesia suppresses the reflexes that normally protect the airway. If the stomach still contains food or liquid, it can be regurgitated and breathed into the lungs. This is called pulmonary aspiration and can cause pneumonia or, rarely, more serious harm.

Fasting rules assume a stomach that empties at a normal rate. In someone taking a GLP-1 medicine, food may remain for longer than expected. Studies using gastric ultrasound and reports from endoscopy have found residual stomach contents more often in people taking these medicines, despite standard fasting. Reported rates of actual aspiration remain low, and the size of the extra risk is still debated, but it is enough for anaesthetists to want to know.

What UK guidance says

MHRA Drug Safety Update, January 2025

The MHRA's Drug Safety Update on GLP-1 and dual GIP/GLP-1 receptor agonists highlighted the potential risk of pulmonary aspiration during general anaesthesia or deep sedation. Key points included:

• Anaesthetists should assess aspiration risk in patients taking these medicines.
• People may have obtained these medicines privately for weight loss and might not mention them unless asked.
• Use should ideally be identified at pre-operative assessment.
• The UK SmPCs did not give guidance on withholding these medicines before surgery.
• Patients should tell their healthcare team if they take one of these medicines and should not stop without medical advice.

The 2025 UK multidisciplinary consensus

In 2025 the journal Anaesthesia published a consensus statement on the elective perioperative management of adults taking GLP-1 receptor agonists, GIP/GLP-1 agonists and SGLT2 inhibitors. It was produced by eight UK organisations: the Association of Anaesthetists, the Association of British Clinical Diabetologists, the British Obesity and Metabolic Surgery Society, the Centre for Perioperative Care, the Joint British Diabetes Societies for Inpatient Care, the Royal College of Anaesthetists, the Society for Obesity and Bariatric Anaesthesia and the UK Clinical Pharmacy Association.

In summary, it advises that:

• People taking GLP-1 or dual GIP/GLP-1 medicines should generally continue them before elective surgery, rather than routinely stopping them.
• Each patient should have a full risk assessment and stratification.
• Techniques that reduce aspiration risk should be used before, during and after sedation or general anaesthesia.
• Risk and the options for reducing it should be discussed with the patient through shared decision-making.

The reasoning is that stopping these medicines has its own downsides. For people with type 2 diabetes, it can worsen blood glucose control around the time of surgery, which itself raises the risk of complications. For people taking them for weight management, a gap can bring back appetite and may mean restarting at a lower dose afterwards. Stopping a weekly injection a week or two in advance also does not reliably return stomach emptying to normal.

Why advice has differed internationally

Earlier guidance from some international bodies, including a 2023 American Society of Anesthesiologists statement, suggested withholding weekly GLP-1 injections for a week before elective procedures. A later US multi-society guidance document in 2024 moved towards individual risk assessment, with a liquid diet beforehand as one option. If you read different advice online, this is likely why. In the UK, follow the instructions of your own hospital team, which will reflect UK guidance and local protocols.

Who is at higher risk

The UK consensus and other guidance describe factors that may increase the chance of food remaining in the stomach. These include:

Some guidance suggests particular care in the first 12 weeks or so of treatment, when stomach-emptying effects may be greatest. If you are about to start a GLP-1 medicine and have an operation coming up, it is worth discussing timing with your prescriber and surgical team before you begin.

What might happen in practice

Every hospital adapts national guidance to its own setting, but you may encounter some of the following.

At pre-assessment

You will usually be asked about all your medicines. Be specific:

• the medicine name, such as Mounjaro, Wegovy, Saxenda, Ozempic or a GLP-1 tablet
• your current dose and how often you take it
• the day of your last dose and when you started
• when your dose was last increased
• any stomach symptoms you have had recently
• whether you obtained it through the NHS, a private clinic or an online provider

If you are treated by an online provider, it is helpful to have the prescription details to hand.

A liquid diet beforehand

One risk-reduction measure described in UK guidance is a liquid-only diet for around 24 hours before the procedure, followed by the usual fasting rules. The idea is to reduce the amount of solid food that could remain in the stomach. You will be told exactly what you can and cannot have and when. Not every patient will be asked to do this, and your team's instructions take priority.

On the day

Your anaesthetist may:

• ask about symptoms again
• use a point-of-care ultrasound scan to check whether the stomach is empty
• choose an anaesthetic technique that protects the airway more quickly, sometimes called rapid sequence induction
• consider regional or local anaesthesia, if suitable for the procedure
• in some cases, postpone a non-urgent procedure if there is clear evidence of a full stomach

These are clinical decisions for the anaesthetist, based on your individual situation.

Endoscopy and sedation

The aspiration concern also applies to deep sedation, which is used for some endoscopies. For an upper endoscopy (gastroscopy), retained food can also make it difficult to examine the stomach properly, which may mean a repeat procedure. Tell the endoscopy unit about your medicine as soon as you receive the appointment. For colonoscopy, bowel preparation instructions are designed to clear the large bowel, and your unit will advise on any additional steps.

Specific situations

Type 2 diabetes

If you take a GLP-1 medicine for type 2 diabetes, perioperative care will also focus on blood glucose. The same UK consensus covers SGLT2 inhibitors, a different class of diabetes medicine (such as dapagliflozin or empagliflozin), which are usually paused around surgery because of a risk of a serious complication called ketoacidosis. Your diabetes and surgical teams will give you a written plan for each medicine. Our guide to GLP-1 medication and type 2 diabetes has more background.

Weight loss surgery

Some people use GLP-1 medicines before bariatric surgery to help reduce weight or liver size, and some use them afterwards. Bariatric teams have their own protocols. Our guide to GLP-1 medication vs bariatric surgery compares the two approaches.

Dental treatment

Routine dental work under local anaesthetic does not carry the same concern, because airway reflexes are not suppressed. Dental procedures under deep sedation or general anaesthetic are different, so mention your medicine to the dental team.

Emergency surgery

In an emergency there is no time for a liquid diet or planned changes. This is one reason it helps if your GP record shows your GLP-1 treatment, even if it is privately prescribed. If you are able to, tell the emergency team which medicine you take and when your last dose was.

GLP-1 tablets

Two GLP-1 tablets are now licensed for weight management in the UK: oral semaglutide (Wegovy tablets), approved by the MHRA in June 2026, and Foundayo (orforglipron), approved in August 2026. The UK consensus applies to GLP-1 receptor agonists irrespective of whether they are taken daily or weekly. Oral semaglutide slows stomach emptying in the same way as the injection. Orforglipron is a newer, non-peptide molecule, and perioperative experience with it is limited at the time of writing. Treat either tablet in the same way: declare it and follow individual advice. Our oral GLP-1 guide explains the tablets.

If you are told to pause your medicine

Some teams may still advise pausing treatment in specific circumstances. If that happens:

• Ask exactly which dose or doses to skip.
• Ask when to restart and at what dose.
• Let your prescriber know, especially if you are treated by an online provider.

The SmPCs for Mounjaro and Wegovy give rules for missed doses, and a longer gap may mean restarting at a lower dose to reduce side effects. Our guide to a Mounjaro missed dose explains how this works. Your prescriber should make that decision, not you alone.

After surgery

Recovery from surgery can bring nausea, reduced appetite and constipation, especially if you are given opioid painkillers. GLP-1 medicines can add to all three. Practical points:

• Hydration: aim to keep fluids up, as dehydration can strain the kidneys. See our hydration guide.
• Nutrition: protein supports wound healing. Small, frequent meals may be easier.
• Bowels: constipation is common after surgery and on GLP-1 medicines. Our constipation guide offers practical steps.
• Restarting: if you paused your medicine, restart only as advised. Restarting at a high dose after a gap can cause marked nausea.

Understanding the evidence

It helps to know why guidance has shifted, because it explains why your team may take a particular approach.

What studies have looked at

Most of the evidence comes from three types of study:

• Gastric ultrasound studies, in which an anaesthetist scans the stomach before a procedure to see whether it contains food or a large volume of liquid. Several of these found residual contents more often in people taking GLP-1 medicines than in those who were not, despite standard fasting.
• Endoscopy studies, which look back at upper endoscopies and record how often retained food was found. Again, retained food was reported more often in people on GLP-1 medicines.
• Large database studies, which look for coded diagnoses of aspiration or aspiration pneumonia after procedures. These have produced mixed results. Some suggested a small increase in risk; others found little or no difference once other factors were taken into account.

The overall picture is that food is more likely to be left in the stomach, but actual harmful aspiration remains rare. That is why UK guidance focuses on identifying and managing the risk, rather than routinely stopping treatment.

What is still uncertain

Several questions remain open at the time of writing:

• how long the effect on stomach emptying lasts at a stable dose, and whether it fades fully
• whether the risk differs between semaglutide, tirzepatide, liraglutide and the newer tablets
• the ideal length and content of any pre-procedure liquid diet
• how risk varies with the type of procedure and anaesthetic

Guidance may be updated as more evidence becomes available. Your hospital will apply the current version.

Planning ahead if you are considering treatment

If you are thinking about starting a GLP-1 medicine and already know you have an operation coming up, it is worth raising this with the prescriber before you begin. Things to consider together include:

• Timing. Because stomach-emptying effects may be strongest in the first weeks and after dose increases, some people and their clinicians prefer to wait until after a planned procedure to start, or to avoid increasing the dose shortly beforehand.
• The purpose of the operation. For some planned operations, such as joint replacement, surgeons may want weight to be lower first. In that case, treatment may be part of the preparation, and the surgical team should be involved in the plan.
• Diabetes control. If you have type 2 diabetes, good blood glucose control before surgery matters, and a GLP-1 medicine may be part of achieving that.

A reputable prescriber, whether NHS or private, should ask about upcoming procedures as part of the consultation. Our guide to the online weight loss consultation describes what a thorough assessment includes.

Questions you might ask your team

Pre-assessment appointments can feel rushed. Writing down a few questions can help:

1. Should I continue my GLP-1 medicine as normal before the procedure?
2. Do I need a liquid diet beforehand, and if so, for how long and what can I have?
3. What are my fasting times for food and for clear fluids?
4. Will I have a general anaesthetic, sedation or a local or regional anaesthetic?
5. If I have nausea or bloating in the days before, who should I tell?
6. When can I take my next dose after the procedure?
7. Do any of my other medicines need to change around the operation?

There are no wrong questions. Anaesthetists would rather know about your medicine and your symptoms than find out on the day.

Common misunderstandings

A note on telling your GP

The MHRA has specifically flagged that people obtaining weight loss medicines privately may not mention them to healthcare professionals. Regulated online providers usually ask for your GP's details so they can share information, and you can choose to tell your GP directly as well. This makes it more likely that the medicine appears on your record if you need unplanned surgery. Our guides to how to choose an online pharmacy and who regulates online weight loss services explain what responsible providers should do. You can also see how regulated providers compare on our provider comparison page.

Summary: practical checklist

For related reading, browse our safety guides, or visit our hubs for weight loss injections and oral GLP-1 tablets.

When to speak to a professional

Contact your surgical pre-assessment team or prescriber if:

• you have a procedure booked and have not yet been asked about your GLP-1 medicine
• you are about to start a GLP-1 medicine and have surgery coming up
• you have been given conflicting advice about whether to continue
• you have nausea, vomiting, bloating or reflux in the days before your procedure

After surgery, seek urgent medical help (call NHS 111, or 999 in an emergency) if you have:

• severe or persistent abdominal pain, which may spread to your back, with or without vomiting
• breathlessness, a cough with fever, or chest pain after an anaesthetic, which could indicate a chest infection or aspiration
• persistent vomiting with inability to keep fluids down, or very little urine
• confusion, drowsiness or signs of severe dehydration

Suspected side effects can be reported to the MHRA through the Yellow Card scheme.