Medical Research News

Cannabis and Anesthesia: Potential Interactions?

Written by Loren DeVito, PhD

Bring your cannabis use out before you go under

Patients lie. That’s a well-known fact to health care professionals. In fact, they expect that answers to questions during a medical exam will be, at best, half true. But why?

There are a few reasons why people lie about their health. [1] One is to avoid being chastised about habits like smoking, eating a poor diet, or having a sedentary lifestyle. Another reason for lying is completely unintentional – it’s simply difficult to remember everything you experienced in the months (if not years) between visits.

Despite patient-physician confidentiality, people may be afraid to disclose sensitive information like illness status or medication/substance use, especially when this information could result in legal ramifications. And prior to the advent of (semi-) legalization, cannabis met this criterion.

But cannabis can interact with medications and change how they affect you. And when it comes to surgery, cannabis use history can influence how your procedure might be planned.

Prior to most surgeries, you’ll need to be “put under” — a common euphemism for anesthesia. There are several different types of anesthetics but they all work in a similar way to numb pain and help muscles relax. Your anesthesiologist has the very important job of keeping you safely “out” and making sure your vital signs remain stable.

Early research in the 1970s indicated that tetrahydrocannabinol (THC) consumption within 72 hours prior to anesthesia for oral surgery was associated with cardiovascular effects possibly due to medication interactions. [2] Additional studies have shown that cardiovascular or respiratory side effects resulting from anesthesia may differ depending on cannabis use history — meaning that long-term users have higher levels of cannabinoids in their body, but also may experience blunted acute effects. [3]

These safety considerations are quite relevant as legalization spreads. So what can we learn from patients in fully legal states who may (potentially) be more forthcoming about their cannabis use?

Researchers recently examined this issue in Colorado, where recreational cannabis use has been legal since 2012. [4] A retrospective study reviewed 250 medical cases of patients who underwent an endoscopy (procedure used to study the digestive system). Those who consumed cannabis daily or weekly were considered “regular cannabis users,” and those who consumed it sporadically or not at all were considered “nonusers.”

The study found that cannabis users required significantly higher doses of anesthetics compared to non-users — in fact, they needed 14% more fentanyl, 19.6% more midazolam, and 220.5% more propofol. While the authors admitted the mechanisms underlying these effects are unknown, these are certainly large differences.

It’s important to note that there were far fewer cannabis users (25) compared to non-users (225), which could have significantly affected the statistical outcomes. This study was also retrospective in nature and therefore confounding factors could have affected response to anesthetics. There is also no information available on the type of cannabinoids consumed, doses, or method of administration. [4]

While greater research is certainly needed, it’s not a bad idea to be upfront about your medical information. The American Society of Anesthesiologists recommends that patients discuss any and all medications they are taking, including supplements; any health conditions or past history of a stroke or heat stroke, or reaction to anesthesia; and if you snore, drink alcohol, smoke cigarettes, and, of course, use cannabis.

Be honest, be safe, and, when in doubt, ask your physician.

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  1. Palmieri, J.J., Stern, T.A. “Lies in The Doctor-patient Relationship.” Prim Care Companion J Clin Psychiatry, vol.11, 2009, pp. 163-168. (impact factor: NA; cited by: 27)
  2. Gregg, J.M., et al. “Cardiovascular Effects of Cannabinol During Oral Surgery.” Anesth Analg, vol.55, no. 2, 1976, pp. 203-213. (impact factor: 3.827; cited by: 27 (Google Scholar))
  3. Alexander, J.C., Joshi, G.P. “A Review of the Anesthetic Implications of Marijuana Use.” Proc (Bayl Univ Med Cent), vol.32, no.3, 2019, pp. 364-371. (impact factor: N/A; cited by: NA)
  4. Twardowski, M.A., et al. “Effects of Cannabis Use on Sedation Requirements for Endoscopic Procedures.” J Am Osteopath Assoc, 2019, ePub. (impact factor: N/A; cited by: NA)

About the author

Loren DeVito, PhD

Loren DeVito, PhD is a neuroscientist and science writer with expertise in cannabis science and medicine. She is committed to communicating evidence-based information about cannabis and its healing properties. Learn more about her work at

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