Cannabis use and anaesthetic agent dosing in patients undergoing surgery or interventional procedures: a single-centre retrospective cohort study.

Ratajczak N.; Ahrens E.; Wachtendorf L.; Munoz-Acuna R.; Redaelli S.; Suleiman A.; Seibold E.; Hentges M.; Tenge T.; von Wedel D. et al. · British journal of anaesthesia · 2026

**Background & Methods** This single-centre retrospective cohort study analysed 341,199 adult patients undergoing propofol sedation or volatile-based general anaesthesia at Beth Israel Deaconess Medical Center (2008-2024). Cannabis exposure was categorised as medical (certified use) or non-medical (recreational use/cannabis use disorder), with primary outcomes measuring propofol dosing (μg kg⁻¹ min⁻¹) and volatile anaesthetic minimum alveolar concentration (MAC) values. **Key Findings** • Both non-medical and medical cannabis users required significantly increased anaesthetic doses: non-medical users needed +6.85 μg kg⁻¹ min⁻¹ propofol (95% CI 6.07-7.63, P<0.001) and +0.01 MAC volatile anaesthetic; medical users required +2.87 μg kg⁻¹ min⁻¹ propofol (P=0.005) and +0.02 MAC volatile anaesthetic (P=0.002). • Dose-response relationship observed, with daily recreational cannabis users showing the strongest effect (+8.41 μg kg⁻¹ min⁻¹ propofol, 95% CI 7.00-9.81, P<0.001), suggesting frequency-dependent anaesthetic resistance. • Cannabis-using patients experienced greater intraoperative cardiovascular response, with increased heart rate post-intubation (+1.45 beats min⁻¹, 95% CI 1.10-1.79, P<0.001) despite comparable induction doses. **Dosage & Administration** Propofol requirement increases in cannabis users: non-medical users +6.85 μg kg⁻¹ min⁻¹; medical users +2.87 μg kg⁻¹ min⁻¹; daily recreational users +8.41 μg kg⁻¹ min⁻¹. Volatile anaesthetic MAC increases: non-medical +0.01 MAC; medical +0.02 MAC. **Safety & Adverse Effects** Greater heart rate elevation during tracheal intubation in non-medical cannabis users (+1.45 beats min⁻¹) was documented; however, comprehensive perioperative complication rates were not detailed. **Evidence Quality** This large retrospective cohort study provides robust evidence from >340,000 patients, supporting previously reported cannabis-anaesthetic interactions. However, limitations include observational design (causality cannot be established), potential unmeasured confounders, and lack of standardised cannabis exposure quantification regarding frequency, potency, or time since last use. Effect sizes were notably smaller than historical reports, and authors acknowledge that clinical relevance of observed dosing differences requires future investigation. The study does not evaluate patient safety outcomes or long-term complications.

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