Do I have to tell my anaesthetist about my prescription?

There is no law on this

The short answer

There is no law requiring it, and a clear clinical reason to do it. Published anaesthesia research has repeatedly found that regular cannabis users need measurably more anaesthetic agent to reach the same depth, and report more pain afterwards. Your anaesthetist cannot plan around what they have not been told.

General information, not advice. This page describes the law as at the last-checked date shown at the foot of it. It does not take your circumstances into account, and small differences in circumstances change outcomes. If a decision turns on this, speak to someone qualified about your own situation.

What the law actually says

No Australian statute governs telling a treating clinician about a prescribed medicine. This is a clinical safety question rather than a legal one, which is why this page cites medical literature instead of legislation.

What that literature says. A 2025 systematic review and meta-analysis pooling eight studies and 2,268 patients found propofol requirements significantly higher in cannabis users, both under general anaesthesia and for endoscopic sedation. A 2024 review in Anesthesia & Analgesia reports that clinical studies and case reports consistently show increased requirements for GABAergic anaesthetic drugs — isoflurane, sevoflurane, propofol and midazolam — and that human data shows cannabis users reporting higher postoperative pain scores and needing more opioid analgesia. A 2026 review adds that responses to opioids, ketamine and gabapentinoids may also differ, with proposed mechanisms including cytochrome P450 induction and CB1 receptor downregulation.

The practical conclusion those authors draw is the one this page makes: a 2020 review in Schmerz recommends that patients be asked before an operation about medical or recreational cannabis use. If you are not asked, tell them anyway.

This page deliberately quotes no doses. The figures in those studies describe what an anaesthetist administers, not anything you should do, and the whole point is that the decision belongs to the clinician who has the full picture.

What happens if it goes wrong

Withholding it means your anaesthetic is planned on incomplete information. The literature above does not suggest surgery is routinely cancelled because a patient discloses a prescription — it suggests the plan is adjusted. VERIFY: an Australian anaesthetist should confirm that cancellation statement reflects practice here before this page is published.

What to carry

Your pharmacy label, or a list naming the medicine, its strength and how often you take it.
The name and contact details of your prescriber.
The printable card at /tools/surgery-card/, filled in.

What to say

Tell the pre-admission clinic, not only the surgeon — your anaesthetist is usually a different person you meet on the day.
Say how often and how recently you have taken it, not just that you hold a prescription. Regularity is what the research turns on.
Mention it even if you have been asked to stop before surgery, and say when you actually last took it.

What not to do

Do not change or stop your dose on your own before surgery. Ask the person who prescribed it.
Do not assume it is already in your file. Say it out loud.
Do not downplay how often you take it. Under-reporting is the thing that makes the anaesthetic plan wrong.

Sources

Baker MB et al., 'Quantitative Analysis of Propofol Dosage in Cannabis Users: A Systematic Review and Meta-Analysis', J Clin Med 2025;14(3):858 academic checked 2026-08-11
Echeverria-Villalobos M et al., 'Cannabinoids and General Anesthetics: Revisiting Molecular Mechanisms of Their Pharmacological Interactions', Anesth Analg 2024;140(6):1401-1413 academic checked 2026-08-11
Mann DK, Portnof J, Adlesic E, 'Marijuana Use and Its Impact on Outpatient Anesthesia', Anesth Prog 2026;73(1):53-64 academic checked 2026-08-11
Kraft B, Stromer W, 'The effects of cannabis and cannabinoids on anesthesia and analgesia during the perioperative period', Schmerz 2020;34(4):314-318 academic checked 2026-08-11

Cite this page

Know Your Script, ‘What your anaesthetist needs to know before surgery’ (Australia-wide), https://www.knowyourscript.com.au/surgery/telling-your-anaesthetist/ (UNVERIFIED DRAFT — not checked, not for citation).

This page has not been checked by anyone. Please do not cite it.

Last checked: DRAFT — never verified