Key takeaways
- Australia's anaesthesia college warned on October 5 that people using GLP-1 injections or other weight-loss peptides should tell their anaesthetist before surgery.
- A large UK study found regurgitation under anaesthesia was about 11 times more common in GLP-1 users, though the absolute risk stayed small.
- Unapproved products like research-grade retatrutide carry the same stomach-slowing concern, plus no regulated labeling to warn anyone.
- Doctors stress: don't stop a prescribed medicine on your own. Tell your surgical team what you take, when and why.
GLP-1 drugs slow down how fast the stomach empties. That's part of how they curb appetite, but it also means food can still be in the stomach after a standard pre-surgery fast. This week, anaesthetists in Australia and New Zealand put that risk front and center, and they named unapproved peptides specifically 12.
The message matters beyond Australia. Many people now get these drugs online or as research vials, and some don't mention them before a procedure. The warning is simple: your anaesthetist needs to know.
What the anaesthesia college said this week
The Australian and New Zealand College of Anaesthetists (ANZCA) issued its warning on October 5, ahead of National Anaesthesia Day 1. President Dr Tanya Selak said the medicines "can slow the emptying of the stomach," and that anaesthetists need to know what a patient takes, when they last took it, and why.
ANZCA told patients not to stop their medication without medical advice. Standard fasting means no solid food for six hours before elective surgery, but GLP-1 users may get different instructions, such as fluids only from the day before 13. ABC News reported that some patients skip mentioning their use because they forgot, feel embarrassed, or bought unapproved peptides 2.
The UK study behind the warning
The numbers come from a national study in the journal Anaesthesia, published September 16 (background context) 4. Researchers screened 47,039 surgical patients at 119 UK hospitals. About 2.9% were taking a GLP-1 drug such as Tirzepatide (Mounjaro) or Semaglutide (Ozempic, Wegovy).
Regurgitation or aspiration happened in 0.12% of non-users, roughly 1 in 802. In GLP-1 users it was 1.41%, roughly 1 in 71: about 11 times higher 4. Most events in GLP-1 users happened while waking up, not at the start of anaesthesia.
The authors were careful. The study can't prove the drugs caused the events, because obesity and diabetes raise aspiration risk on their own 4. Over 40% of GLP-1 users got their prescriptions outside their usual doctor, such as from online pharmacies.
Why unapproved peptides are a special problem
Retatrutide is not approved anywhere. Its MyPeps entry lists it as investigational, with Lilly planning an FDA filing around early 2027. Like tirzepatide, it slows stomach emptying, and ABC's report named it among the self-injected products anaesthetists worry about 2.
The issue isn't only the drug. An approved pen comes with a label, a prescriber and a pharmacy record. A research vial has none of that, so nobody on the surgical team may know it exists unless the patient says so.
Retatrutide also has a long half-life of about 6 days. Expert Michael Horowitz told ABC that slowed gastric emptying can persist, and called the common advice to stop a week before surgery "demonstrably stupid" 2. How long the effect lasts after stopping still needs research.
Quick hits from the week
Retatrutide's TRIUMPH-2 paper is now indexed. The Lancet trial in 1,152 adults with obesity and type 2 diabetes came out online September 29 and reached PubMed this week (background context) 56. At 80 weeks the 12 mg dose cut body weight by 18.8% versus 5.1% on placebo. Skin-sensation changes (dysesthesia) hit up to 7% versus 1% on placebo, and low blood pressure events reached 6% at the top dose 6.
A tanning peptide and a new melanoma. A case report covered by Gizmodo on October 8 describes a 46-year-old man who developed a new early melanoma weeks after daily Melanotan II injections bought at a gym 7. He also used tanning beds and had a prior skin cancer, so the authors couldn't rule out other causes.
Stem cell sellers want the "peptide path." STAT reported on October 5 that stem cell entrepreneurs see the FDA's softer stance on compounded peptides as a model for their own products 8. The FDA declined to say whether new roundtables are planned.
GLP-1 drugs and retatrutide compared
| Peptide | What it is | FDA status | Evidence (1–5) | Half-life | Banned in sport |
|---|---|---|---|---|---|
| Semaglutide | GLP-1 agonist (Ozempic, Wegovy) | Approved | 5 | About 7 days | No (WADA monitoring) |
| Tirzepatide | GIP/GLP-1 agonist (Mounjaro, Zepbound) | Approved | 5 | About 5 days | No (WADA monitoring) |
| Retatrutide | GIP/GLP-1/glucagon triple agonist | Not approved (phase 3) | 4 | About 6 days | Yes (S0) |
| Melanotan II | Non-selective melanocortin agonist | Not approved | 3 | About 1 hour or less | Yes (S0) |
The bottom line
GLP-1 drugs and related peptides can leave food in the stomach even after a normal fast. The absolute risk is small, but it is real enough that anaesthetists want to be told, whether the drug came from a pharmacy or a research vial. Telling your surgical team is the fix, and stopping on your own is not.
This is educational information, not medical advice.
Sources
- Warning on weight-loss injections and peptides for patients having surgery — ANZCA via Medianet, October 5, 2026. https://newshub.medianet.com.au/2026/10/warning-on-weight-loss-injections-and-peptides-for-patients-having-surgery/174819/
- Weight-loss GLP-1 jabs like Ozempic and unapproved peptides pose 'serious' surgery risk — ABC News, October 7, 2026. https://www.abc.net.au/news/2026-10-07/peptides-ozempic-surgery-warning/107233212
- GLP-1 receptor agonists: clinical practice recommendations — ANZCA. https://www.anzca.edu.au/safety-and-advocacy/standards-of-practice/clinical-practice-recommendations-regarding-patients-taking-glp-1
- Peri-operative glucagon-like peptide-1 receptor agonist use and outcomes: a national prospective multicentre cohort study (El-Boghdadly et al.) — Anaesthesia, via EurekAlert, September 16, 2026. https://www.eurekalert.org/news-releases/1144100
- Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a phase 3 trial — The Lancet, September 29, 2026. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(26)01861-1/abstract
- New triple agonist retatrutide produces substantial weight loss in people living with obesity and type 2 diabetes — EurekAlert, September 29, 2026. https://www.eurekalert.org/news-releases/1145754
- Man injects gym-bought tanning peptide, gets a new melanoma — Gizmodo, October 8, 2026. https://gizmodo.com/man-injects-gym-bought-tanning-peptide-gets-a-new-melanoma-2000823544
- Are stem cells the next peptides? These advocates think RFK Jr. could make it happen — STAT, October 5, 2026. https://www.statnews.com/2026/10/05/stem-cell-industry-seeks-fda-regulation-like-peptides/