We’ve said “talk to your doctor about cannabis” before, and meant educate your GP about its benefits for salving or managing illnesses. But there are other reasons to talk to other doctors about cannabis too, even recreational use: cannabis conflicts with medications.

I came across a Tumblr post recently warning people to cop to using cannabis to anesthesiologist … so you don’t wake up during surgery. Pretty frightening since I’m facing surgery and had no idea this was even a thing — I’ve never been anaesthetized while a regular cannabis user.

But Tumblr isn’t a reliable medical resource, so I went looking for professional evidence. And found even more examples of cannabis conflicts with medications. I’m not a medical scientist, so some of it went over my head — but boy is there reason to talk to your doctors about any cannabis use, if you’re gonna be taking regular medication or are going under general anaesthetic.

Cannabis Conflicts with Medications

Activists fought to access medical cannabis because we know cannabis has medical uses — which means it has medical conflicts as well. Just because it’s natural and contains chemicals similar to what our bodies produce doesn’t make cannabis harmless; chemicals interact with other chemicals, after all. Just think about what happens when you mix a little cannabis and a little alcohol: you can get a lot faded. Cannabis is safe alone, but not necessarily safe with other substances.

We have to consider how cannabinoids affect the way our body metabolizes other medications. We need those medications to work how our doctors expect them to. (And cannabis users also probably want to know what medications decrease and increase the effects of cannabinoids.)

Impact on Medication

Unfortunately, prohibition continues to make it hard to research cannabis and its impacts on other medications. But we know its interactions with the body’s metabolizing enzymes. Potentially, cannabis conflicts with medications because of those effects.

Regular cannabis use is thought to induce the enzyme responsible for metabolizing caffeine, estradiol/estrogen, lidocaine, and melatonin, among others. Inducing doesn’t mean the drug’s effects are positively induced, it means metabolizing the drugs faster. Meaning chemicals have less time to affect your body: i.e. you get over them quicker. So cannabis may make these drugs less effective with regular use.  

CBD is also known to impact various epilepsy medications, increasing some concentrations and decreasing others. As epilepsy is also treated with cannabis, it’s important that doctors are aware of cannabis use for anyone also using these medications.  

Impact on Cannabis

There are a bunch of medications that induce the enzymes that metabolize cannabinoids, decreasing strength and duration of a high. Barbiturates, phenobarbital specifically noted, St John’s Wort, and others may induce THC and CBD metabolism.

Inhibitors are the opposite of inducers. They stop your body from metabolizing a drug, meaning its effects could be stronger or longer than expected. The metabolic inhibitors that increase the duration of cannabinoid effects are interesting. As well as clarithromycin (antibiotic) and antifungal meds, inhibitors include antiretrovirals used to treat HIV/AIDS, antivirals used to treat Hepatitis C, a variety of SSRIs/antidepressants … and grapefruit juice.

Obviously the only interaction I’d suggest trying intentionally to slow cannabinoid metabolism is the grapefruit juice!

There are also medications that can increase unwanted side effects of cannabis. For example, drugs that stimulate the sympathetic and parasympathetic nervous systems can increase cannabis-caused high heart rates and high blood pressure. Talk to your doctors.

Cannabis Conflicts with Anaesthesia

As well as expected interactions because of enzymes, there are known cannabis conflicts with medications that impact anaesthesia. The same way that cannabis and alcohol increase each other’s effects, drugs that relax us (central nervous system depressants) are more relaxing with cannabis. And that’s not necessarily a good thing when we’re going beyond a daily Xanax, and going under on the operating table.

But while one might think “increased effects” of benzodiazepines and barbiturates would mean cannabis would help patients drift off easier, that’s not necessarily the case. Blood pressure and heart rate can increase from cannabis use, and that can impede the drugs used to knock you out. Or the drugs used to try and knock you out could spike your heart rate or blood pressure, causing your medical team a lot of worry and possibly ending your surgery before it can begin.

Cannabis conflicts with medications used for anaesthesia also seem to be both dosage and use dependent. A chronic toker and someone who smoked for the first time before surgery to “take the edge off” would not have the same interactions with anaesthesia drugs.

Because cannabis itself somewhat mimics the effects of anaesthetic drugs, long-term or heavy use may make the body more used to those effects, meaning a harder time for your anaesthetist. 

As well, although there’s no evidence that cannabis smoking causes cancer like cigarette smoking does, it does lower breathing function and certainly impacts the airways that anaesthetists need to keep open and fill with anaesthetic.

Was Tumblr Right?

This pseudo-anaesthetic action explains the fitfulness in going under and possibly staying under, which could result in waking in the middle of surgery.

But the warning from the anaesthesiologists on Tumblr aside, I couldn’t find medical reports of people waking up on the operating table because they smoke pot. That could be because it’s never happened, because no one wants to admit it happens, or because doctors prefer to go off of medical studies. But there are documented cases of the difficulty in sedating cannabis users, so for that alone it’s worth telling your doctors you consume cannabis.

Don’t smoke before surgery, it will not help anaesthetic. Do tell your anesthesiologist that you consume cannabis so they can provide the right drug and dose. And of course it should go without saying, do not consume anything in the time period demanded before surgery or you could be forced to reschedule. (But do consume cannabis as a recovery painkiller!)

Feature Image of @ziicka and @JolieHoliday by MaryBeth Lafferty Photography for Twelve High Chicks.


Stirring the Pot: Potential Drug Interactions With Marijuana; Sarah T. Melton, PharmD; 2017.

Anaesthetic Consideration in a Cannabis Addict; Karima Karam, Shemila Abbasi and Fauzia Anis Khan; 2015.

Cannabis consumption before surgery may be associated with increased tolerance of anesthetic drugs: A case report; Georg Richtig, Götz Bosse, Friederike Arlt, Christian von Heymann; 2015.

Medical Cannabis Adverse Effects & Drug Interactions (PowerPoint); Government of DC, DOH; 2015.

Anesthetic management of the illicit-substance-using patient; Marcelle Hernandez , David J. Birnbach, and André A.J. Van Zundert; 2005.

Cannabis smoking and anaesthesia; I. E. Symons; 2002.

The Effects of Δ1-Tetrahydrocannabinol and Other Cannabinoids on Spin-Labeled Liposomes and Their Relationship to Mechanisms of General Anesthesia; D.K. Lawrence and E. W. Gill; 1975

Interaction of cannabis and general anaesthetic agents in mice; G.B. Chesher, D.M. Jackson, and G.A. Starmer; 1974.