Background and objective: An estimated 150 million people worldwide use cannabis. The effect of cannabis on anaesthetic requirements in humans does not appear to have been studied.Methods: In this prospective, randomized, single-blinded study, 30 male patients using cannabis more than once per week (group C) and 30 nonusers (group NC), aged 18-50 years, were induced with propofol 1.5, 2, 2.5, 3 or 3.5 mg kg-1. Additional doses were given when required. The primary outcome was the 50% effective dose of propofol and successful induction was determined by loss of consciousness with a bispectral index value of less than 60 and satisfactory insertion of a laryngeal mask. Propofol requirements to achieve these outcomes were recorded.Results: The dose required to achieve the target bispectral index value was not significantly higher in group C, but group C required a significantly higher propofol dose to achieve laryngeal mask insertion (314.0 ± 109.3 vs. 263.2 ± 69.5 mg, P <0.04). The estimated effective propofol induction dose in 50-95% of patients did not significantly differ between groups.Conclusion: We conclude that cannabis use increases the propofol dose required for satisfactory clinical induction when inserting a laryngeal mask.