As more states legalize marijuana, surgery centers and anesthesiologists should learn about safety issues related to ingestion of cannabinoids.

Cannabis use matters in the perioperative setting, says Karim Ladha, MD, MSc, assistant professor, anesthesia, University of Toronto. “We took a large national registry of patients coming in for surgery and looked at those with cannabis disorder,” Ladha says. “Those ICD-9 codes for cannabis disorder are picked up in our database.”

When Ladha and colleagues analyzed data for patients with cannabis disorder diagnoses and those without, their overall health outcomes looked similar. But when investigators examined specific complications, they saw a difference between the groups, Ladha says.1

“Those with cannabis disorder had a higher risk of myocardial infarction and risk of stroke,” Ladha says. “This makes sense when we look at cannabis and how it interacts with the cardiovascular system.”

Smoking marijuana affects the cardiovascular system, but less obvious is the effect of tetrahydrocannabinol (THC), marijuana’s active ingredient, on heart rate. There is potential impact on oxygen in the blood, but this is an area that needs more study, Ladha says. Drug interaction of marijuana with anesthesia products also could affect surgical patients.1

“There are some data to suggest that patients who are using cannabis routinely will have higher anesthetic requirements and increased pain postoperatively,” Ladha says. “That data are not robust, but it gives us an idea of challenges.”

Marijuana use can produce a sedative effect and can interact with anesthesia. Also, smoking cannabis carries as many significant risks as smoking cigarettes.2 With chronic use, marijuana cigarettes can lead to lung disease, notes Bridget Petrillo, CRNA, who works for Greater Anesthesia Solutions LLC in Phoenix. Petrillo also is a member of the Peer Assistance Advisors Committee of the American Association of Nurse Anesthetists.

Nurse anesthetists and anesthesiologists can educate patients about the risks of using cannabis and marijuana cigarettes. “It can cause lung disease, which can compromise the patient’s health in being intubated,” Petrillo explains. “We inform patients that marijuana use could impact their requirements for medicine.”

Patients using cannabis might need more anesthesia — and with more anesthesia, they could experience more side effects, Petrillo cautions. Surgery centers could educate patients about the risks of smoking cannabis in the days or weeks leading up to surgery. For instance, surgery patients with damaged lungs from cigarette or marijuana smoking might be at a safety risk if they are put on a machine to mechanically ventilate their lungs, Petrillo says.

Surgery centers and physicians should screen patients for cannabis use and acknowledge potential drug interactions, including with CBD products that are legal even in states that have not legalized marijuana. “There are drug interactions with CBD,” says Kevin Hill, MD, MHS, director, division of addiction psychiatry, Beth Israel Deaconess Medical Center, and associate professor of psychiatry, Harvard Medical School.

CBD is one of the active ingredients of cannabis and is a component of medical marijuana. It also is sold in the United States over the counter as oil concentrates, topical agents, capsules, edibles, tinctures, vape oils, and skin and hair products.3

There is an FDA-approved version of CBD that serves as an anti-epilepsy medicine, Hill says. “Whether you purchase it online or it’s prescribed, there are potential drug-drug interactions,” he adds.4

Physicians will need to ask patients specifically about how they ingest cannabis products. For instance, the rise of vaping’s popularity has led to vaping-related lung injuries, some of which involve THC. “We need to pay more attention to vaping,” says Edward Mariano, MD, MAS, professor of anesthesiology, perioperative and pain medicine, Stanford University. “It’s a real problem ... and we didn’t have it on our radar until recently. We have seen patients who switched from combustible cigarettes to e-cigarettes and vaping devices, and it’s matching with the surge in vaping-related lung injury.”

In a recent report from the CDC, most people affected by an outbreak of lung injury from vaping and e-cigarettes were using THC-based vaping products.5 Also, the CDC analyzed data on the use of THC-containing products, and found a number of counterfeit products. The CDC and FDA recommend people do not use THC-containing e-cigarettes or vaping products.6 “These two phenomena — increased vaping and increased use of cannabinoids — go hand-in-hand, and we need to know more about that,” Mariano says. “There is no clear connection between vaping injury and a specific ingredient.”

Anesthesiologists must think about potential risks when patients who have used cannabis products and/or vaping products receive general anesthesia. “You want to anticipate these problems and, in certain circumstances, you can avoid general anesthesia,” Mariano says. “In our outpatient setting, patients with foot and ankle and wrist or shoulder injury could have more selective anesthetic — nerve blocks, which anesthetize one area of the body.”

Now that vaping has introduced a new level of uncertainty, anesthesiologists should engage in presurgery conversations with patients about what techniques are available to them if the patients are vaping or smoking marijuana, Mariano says.

Another consideration is the risk that occurs when surgery patients combine marijuana with opiates. “There is higher potential risk if patients who use marijuana are driving and are on oxycontin for post-operative pain,” says Ivan Urits, MD, pain medicine fellow, Beth Israel Deaconess Medical Center, Harvard Medical School. “I’d advise patients not to mix the two drugs.” More research is needed before physicians will know for sure about drug/anesthesia-to-cannabis interactions. “The short answer is we don’t really know what the best practices are,” Ladha says. “We have some ideas, based on our experience, but we’re trying to solidify that through an expert panel.”

Ladha is involved with a group of global researchers who are working on consensus-based guidelines for perioperative implications of cannabis. “We’re hopeful we’ll release the guidelines within a year,” he reports.


  1. Goel A, McGuinness B, Jivraj NK, et al. Cannabis use disorder and perioperative outcomes in major elective surgeries: A retrospective cohort analysis. Anesthesiology 2019; Nov 25. doi: 10.1097/ALN.0000000000003067. [Epub ahead of print].
  2. American Society of Anesthesiologists. Eight things to tell your physician anesthesiologist before surgery, March 11, 2019. Available at:
  3. Nunley K. What types of CBD products are available? Medical Marijuana, Inc., Aug. 19, 2019. Available at:
  4. Cannabis drug interactions. Available at:
  5. Perrine CG, Pickens CM, Boehmer TK, et al. Characteristics of a multistate outbreak of lung injury associated with e-cigarette use, or vaping – United States, 2019. MMWR Morb Mortal Wkly Rep 2019;68:860-864.
  6. Centers for Disease Control and Prevention. Outbreak of lung injury associated with e-cigarette, or vaping, products. Available at: