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Cannabis Users May Need More Anesthesia During Surgery – and More Pain Meds After

November 24, 2020
Recent data relates cannabis use to higher pain scores in both the post-anesthesia care unit and the inpatient setting.

As more states have legalized marijuana for medical and/or recreational purposes – especially after the state measure ballots, cannabis use has become more common across the United States with the CDC reporting that 22.2 million Americans use the substance each month.1

Despite a plethora of sociological and health-based studies regarding the effects of cannabis use, there have been few studies digging into how the substance interacts with other medications, such as those delivered in perioperative care (anesthesia) or chronic pain analgesics. Anecdotal evidence has suggested that cannabis users require more propofol at the induction of anesthesia than patients who do not use cannabis.

Ian Holmen, MD, an anesthesiologist at the University of Colorado Hospital, and his colleagues noticed a similar pattern in their patients. “So our question was, ‘Is it the same across all anesthetic types? Or just propofol specifically?’” Dr. Holmen told PPM. His team designed a study to examine that question. They also looked at the amount of pain medication required by cannabis users in the post-operative period.

The initial data was presented at the October 2020 annual conference of the American Society of Anesthesiologists.2 A paper presenting their findings is forthcoming in the December 2020 Journal of Clinical Anesthesia.

Study Design

For this single-site retrospective study, Dr. Holmen and his team reviewed the medical records of 118 patients who had surgery for a broken leg. All subjects included had unilateral tibia fractures and underwent open reduction and internal fixation (ORIF) with intramedullary nail (IMN). The researchers chose this type of surgery because it requires a post-operative in-hospital stay which allowed them to track data on the amount of opioid required post-operatively as well as how patients ranked their pain on a pain scale. All patients were treated at the University of Colorado Hospital in Aurora, Colorado between January 2015 and November 2019. Patients who had polytrauma, chronic pain, or prior opioid use were excluded.

Subjects’ cannabis use was determined through patient self-reports and included any quantity of use prior to the study. The researchers did not record what form of cannabis was used or how it was ingested. A standardized pain numeric rating scale was used to determine pain scores.


Roughly a quarter (25.4%) of the subjects reported prior cannabis use. Cannabis use was not associated with a high dose of induction propofol but the average volume of intraoperative sevoflurane was significantly higher among the cannabis users than among those who did not report prior cannabis use.

In addition, cannabis use was associated with higher pain scores in both the post-anesthesia care unit (PACU) and initially in the inpatient setting. The cannabis users required significantly more pain medications than the control group. However, there was not a significant difference between the two groups in amount of time in the operating room, in PACU, or in inpatient care.

Practical Takeaways

Dr. Holmen cautions that this was not a controlled trial but, rather, an aggregate of 118 case studies. It is better described, he says, as “a hypothesis provoking study.” Nevertheless, he stresses that the important takeaway is that clinicians should ask patients to be forthcoming about their cannabis use prior to any surgical procedures. “A provider just needs to know if the patient uses cannabis or not,” he advises. “It doesn’t matter if it’s a daily situation, just so [providers] are aware that the post-operative and possibly interoperative period are going to appear different in a patient who’s using cannabis than one who is not.”

As Dr. Holmen and his team continue to analyze their data, they are also planning two additional studies. One will investigate whether multimodal pain control in cannabis users can reduce the amount of pain after surgery, and another will explore whether cannabis-consuming individuals have a higher risk of opioid misuse one year after surgery.


See our related Side Chat with Mark Wallace, MD, and where he sees medical cannabis fitting into pain practice.


Last updated on: November 24, 2020
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Chronic Pain and the Short-term Effects of Medical Cannabis
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