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Effect of preoperative cannabis use on perioperative outcomes: a retrospective cohort study
  1. Betty Huiyu Zhang1,
  2. Haris Saud1,
  3. Neil Sengupta1,
  4. Max Chen1,
  5. Devyani Bakshi1,
  6. Liz Richardson1,
  7. Li Wang2,3 and
  8. Harsha Shanthanna2,3,4,5
  1. 1 Michael G. DeGroote School of Medicine, McMaster University, Hamilton, Ontario, Canada
  2. 2 Department of Anesthesia, McMaster University, Hamilton, Ontario, Canada
  3. 3 Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada
  4. 4 Research Institute of St Joes, Hamilton, Ontario, Canada
  5. 5 Michael G. DeGroote Centre for Medicinal Cannabis Research, McMaster University, Hamilton, Ontario, Canada
  1. Correspondence to Dr Harsha Shanthanna, Anesthesia, McMaster University, Hamilton, Ontario, Canada; shanthh{at}


Introduction The reported use of cannabis within surgical population is increasing. Cannabis use is potentially associated with increased harms and varied effects on pain control. These have important implications to perioperative care.

Methods We conducted a retrospective cohort study comparing surgical patients reporting cannabis use preoperatively to control patients with no cannabis exposure, in a 1:2 ratio. To control for confounding, we used a propensity score-matched analysis to assess the adjusted association between cannabis use and study outcomes. Our primary outcome was a composite of (1) respiratory arrest or cardiac arrest, (2) intensive care admission, (3) stroke, (4) myocardial infarction and (5) mortality during this hospital stay. Secondarily, we assessed the effects on pain control, opioid usage, induction agent dose and nausea-vomiting.

Results Between January 2018 and March 2019, we captured 1818 patients consisting of cannabis users (606) and controls (1212). For propensity score-matched analyses, 524 cannabis patients were compared with 1152 control patients. No difference in the incidence of composite outcome was observed (OR 1.06, 95% CI 0.23 to 3.98). Although a higher incidence of arrhythmias (2.7% vs 1.6%) and decreased incidence of nausea-vomiting needing treatment (9.6% vs 12.6%) was observed with cannabis users vs controls, results were not statistically significant. No significant differences were observed with other secondary outcomes.

Conclusion Our results do not demonstrate a convincing association between self-reported cannabis use and major surgical outcomes or pain management. Perioperative decisions should be made based on considerations of dose, duration, and indication.

  • outcomes
  • analgesia
  • postoperative complications

Data availability statement

Data are available on reasonable request from the corresponding author.

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Data availability statement

Data are available on reasonable request from the corresponding author.

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  • Contributors BHZ: acquisition of data, drafting and critical revision, final approval; HS, NS, MC, DB, and LR: acquisition of data; final approval; LW: analysis and interpretation of data, final approval; HS: conception and design; analysis and interpretation of data; final approval.

  • Funding This project received funding from the McMaster Medical Student Research Excellence Scholarship.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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