Cannabis use may complicate surgery by making anesthesia less effective, found a Duke University School of Medicine systematic review and meta-analysis.

The study was led by Ruba Sajdeya, M.D, PhD, a medical instructor in the Duke Department of Anesthesiology, which pointed to cases where marijuana users needed higher doses of common sedatives like propofol to stay under during procedures. The problem presents a need for further research and clinical guidelines in the field.

“Some systematic reviews have estimated that there has been an increase between 30 to 50 milligrams of propofol administered for anesthesia induction for procedural sedation which is about a 15 to 30% increase in what typically would be used,” Sajdeya said. However, Sajdeya noted the causal path for this association has not been confirmed or corroborated.

Given cannabis’s growing prevalence nationwide, these complications are surfacing more frequently in medical settings. The number of surgical patients who report using cannabis has tripled over the past decade, Sajdeya said.

Ineffective anesthesia is only one of several concerns that may arise. Cannabis use may also influence systems beyond the nervous system, most notably the cardiovascular system, by increasing the risk of altering the patient’s heart rate and blood pressure, Sajdeya said. Its impact also extends outside the operating room, where Dr. Sajdeya found that patients who use cannabis can experience an increase in postoperative pain levels and require additional opioid administration for pain management.

Although research has consistently observed a link between cannabis use and complications during anesthesia, a direct causal relationship and the exact interactions between cannabinoids and common anesthesia medications have yet to be established. However, Sajdeya emphasized that it is clear that cannabis can affect how the nervous system responds during surgery.

“There are still limitations in our ability to conduct research involving cannabis, whether it’s related to regulations or ethical considerations,” Sajdeya said. 

Medical research on cannabis faces significant hurdles because of regulatory requirements. The American Society of Anesthesiologists (ASA) has called on the federal government to expand research opportunities, highlighting the urgent need to understand how cannabis affects surgery and anesthesia. 

Another difficulty researchers face is that most health care systems lack a standardized way of recording cannabis use in patient charts, leaving researchers with incomplete or inconsistent data.

In an effort to address this issue, in 2023 Sajdeya and her team developed natural language processing algorithms that scan physicians’ narrative notes in electronic health records and extract preoperative cannabis use status. Although the system improved researchers’ ability to measure exposure, it also came with challenges like errors in documentation and uncertainty about the accuracy of patients’ use disclosure.

New tools, such as Sajdeya’s, can help capture data more effectively, but these developments also underscore how much remains unknown. Without standardized reporting and comprehensive studies, doctors are left with limited guidance on how to manage cannabis use in surgical patients.

“We need more research and more high-quality research to tap into these unanswered questions…to understand the potential risks that might be associated with it,” Sajdeya said. She added that, across the broader scientific community — including researchers at Duke, researchers are encouraging one another to pursue studies that address existing knowledge gaps and shed light on the implications of preoperative cannabis use. 

Until more research provides clear answers, Sajdeya offers another solution that can be implemented immediately: communication between patients and providers about cannabis use in a nonstigmatized way . “We definitely want to empower the ability to have discussions, especially between clinicians and patients,” Sajdeya said.