CBD before an operation: why you must tell your anaesthetist

In 2023, ASRA Pain Medicine, the American society for regional anaesthesia and pain medicine, published the first US consensus guidelines devoted to the perioperative management of patients using cannabis and cannabinoids. They appeared in Regional Anesthesia and Pain Medicine.

The method is worth noting: a committee of thirteen experts, nine questions addressed, and twenty-one recommendations formulated through a modified Delphi procedure requiring more than 75% agreement.

The first point is the most important one for a French reader. The society recommends universal screening for cannabinoid use before surgery, covering the type of product, the date of last use, the route of administration, the quantity and the frequency.

The second is counter-intuitive: the society states that it can come out neither for nor against stopping or tapering cannabinoids in the perioperative period, for want of sufficient data. In other words, the recommendation is not to stop, but to speak up.

The third corrects a widespread intuition: regular users may experience more pain and nausea after surgery, not less, and may require more medication, opioids included. The text finally advises postponing elective surgery where mental state or decision-making capacity is impaired at the time of the procedure, and delaying by at least two hours after smoked cannabis, because of an increased cardiac risk. This last recommendation targets inhaled cannabis, not oral CBD.

The most frequently cited empirical signal comes from a retrospective study published in 2019 in the Journal of the American Osteopathic Association, covering two hundred and fifty records. Regular cannabis users required a significantly higher amount of sedation for endoscopic procedures, and the significance held after adjustment for age, sex and the use of alcohol, benzodiazepines and opiates.

A replication study published in 2024 in Gastroenterology Nursing again found increased propofol requirements in the cannabis group, but no significant difference in recovery time. Its authors conclude on the importance of an open exchange making it possible to establish use before procedural sedation.

These papers deal with cannabis, not specifically with isolated cannabidiol. The distinction matters, and we shall not blur it.

This is the ground on which one must be most rigorous, because approximations are common here. The most reliable source is the summary of product characteristics for Epidyolex, published by the European Medicines Agency.

That document establishes that cannabidiol is a substrate of UGT1A7, UGT1A9 and UGT2B7, and that in vitro data show it inhibits CYP2C19, which may increase the plasma concentrations of medicines metabolised by that isoenzyme. It also indicates that increased exposure to other sensitive P-glycoprotein substrates given orally may occur. Lastly, it recalls that central nervous system depressants, alcohol included, may potentiate somnolence.

A point of honesty is called for: that document lists no anaesthetic agent among the documented interactions, and on the contrary mentions that cannabidiol did not alter exposure to midazolam in an interaction study. To write that CBD modifies the effect of anaesthetics would be an extrapolation. What is established is the enzyme profile, which we set out in our articles on drug interactions and on liver enzymes.

We have found no formal recommendation from the Société française d'anesthésie et de réanimation dealing specifically with cannabis or CBD in the perioperative period. That absence is a finding from a documentary search, not proof of non-existence.

In practice, the pre-anaesthetic consultation is the moment provided for declaring any product consumed, including those sold freely. The question of the date of last intake, incidentally, arises in the same way as it does for a drug test, a subject we address in our article on how long CBD stays in the body. For particular physiological situations, our article on CBD during pregnancy and breastfeeding sets out the same logic of caution.

Should you stop CBD before an operation?

The 2023 American guidelines explicitly state that they can come out neither for nor against stopping or tapering before surgery, for want of sufficient evidence. Their recommendation concerns screening and declaration, not stopping. The decision rests with your doctor and your anaesthetist, to whom you should report your use.

What exactly should you tell the anaesthetist?

The 2023 guidelines list the items to be collected: the type of product used, the date of last intake, the route of administration, the quantity and the frequency. A bottle or a pack brought to the pre-anaesthetic consultation answers most of these questions.

Does CBD interact with anaesthetics?

No interaction with an anaesthetic agent is documented in the European product information for the cannabidiol medicine, which on the contrary mentions an absence of effect on exposure to midazolam. What is established is that cannabidiol inhibits CYP2C19 in vitro and is a substrate of several glucuronidation enzymes, which is reason enough to declare its use rather than pass over it in silence.