Weight-Loss Injections and Surgery: What You Need to Tell Your Team

If you take a GLP-1 weight-loss medicine, tell your surgeon and your anaesthetist well before any operation. These medicines slow stomach emptying, which raises the risk of stomach contents entering the lungs under anaesthesia. Current Australian guidance does not recommend stopping them before elective surgery; instead, it recommends a change in what you eat and drink beforehand, which your anaesthetist will explain.

This topic is also in our free guide, The Weight-Loss Medication Guide. Get it emailed to you

Why anaesthetists need to know

Before a general anaesthetic or deep sedation, you fast so that your stomach is empty. If food remains in the stomach, it can be brought up and breathed into the lungs, a complication called aspiration. The Australian Consumer Medicine Information for Wegovy warns of this risk under general anaesthesia or deep sedation and tells patients to inform their treating team before surgery (Wegovy CMI). The Mounjaro CMI likewise asks you to tell your doctor before surgery or anaesthesia (Mounjaro CMI).

The reason is how the medicines work. A 2025 Australian clinical guideline reports that GLP-1 medicines profoundly slow gastric emptying, with both short-term and ongoing use. It cites case reports of food still in the stomach despite extended fasting after a solid meal eaten 20 hours earlier, and a large study in which these medicines were associated with a higher rate of aspiration pneumonia around procedures (0.83% versus 0.63%) (Hocking et al., Anaesth Intensive Care 2025).

What the 2025 Australian guidance says

In 2025 the Australian Diabetes Society, the Australian and New Zealand College of Anaesthetists (ANZCA), the Gastroenterological Society of Australia and the National Association of Clinical Obesity Services published joint recommendations (Hocking et al. 2025; ADS). In summary:

Do not stop the medicine routinely. Stopping GLP-1 and GLP-1/GIP medicines before elective procedures is not recommended. Missing doses may delay surgery or upset blood glucose control.
Change the diet before surgery. The guidance recommends a clear-fluid diet on the day before the procedure, followed by the standard 6-hour fast on the day of surgery.
“Sip til send” may not suit you. Protocols that allow sips of clear fluid until you are called to theatre may be inappropriate for people on these medicines.
Everyone should be asked. All patients should be asked about these medicines before anaesthesia or sedation and involved in planning for the aspiration risk. Where the precautions have not been followed, the anaesthetist should assume a full stomach.

This is a summary for your understanding, not an instruction. Your anaesthetist will give you specific fasting directions for your operation, and any change to your medicine should be agreed with your prescribing doctor. Practice can also change; the guideline itself may be updated.

What to tell your team

The guideline notes that patients do not always mention these medicines, sometimes because of weight stigma and sometimes because the medicine was obtained outside their usual doctor (Hocking et al. 2025). There is no judgement in the question. Tell your surgeon and anaesthetist:

the name of the medicine and how often you take it
the day you usually take it, and when your last dose was
whether you have recently changed dose, or stopped and restarted
any current nausea, vomiting, reflux, bloating or constipation
whether you have diabetes, and what other medicines you take
who prescribes it, so your teams can communicate if needed

This applies to any procedure under anaesthesia or sedation, including endoscopy, not only body contouring. If you are seeing Dr Kumar, raise it at your first consultation so it is part of planning from the start.

Timing skin surgery after medication-driven weight loss

Anaesthetic safety is one question. The other is whether your weight is ready. The published evidence points to stability rather than a set date:

A stable weight for at least 3 months before body contouring significantly reduced complications in one cohort study (van der Beek et al., Obesity Facts 2011). A review recommends 4–6 months without weight fluctuation (Giordano, Open Access Surgery 2015).
For medication-driven loss, a 2025 review suggests body contouring may be appropriate after about 8–12 months of semaglutide use once weight has plateaued, with caution because weight is often regained if the medicine is stopped (Garbaccio et al., Aesthetic Plast Surg 2025).

Regain after stopping is substantial in trials; see what happens when you stop. So your surgeon will want to know not only that your weight is steady, but whether you plan to stay on treatment. For the full discussion, see when is the right time for skin removal.

Preparing well

Reduced appetite can leave you short on protein and some nutrients at the point you need them most for healing. A review of surgery after massive weight loss recommends pre-operative blood tests including haemoglobin and prealbumin, and gives a peri-operative protein goal of 70–100 g a day (Giordano 2015). See nutrition before body contouring and health checks and investigations. Surgical risks are set out on risks and considerations, and in more detail on drkumar.com.au.

Where to next

If your weight has settled and loose skin is now the main issue, book a consultation with Dr Kumar or take the readiness assessment. Bring a list of your medicines, including any weight-loss injection, to that first appointment.