Cannabis Use Cessation and the Risk of Psychotic Disorders: A Case–Control Analysis from the First Episode Case–Control EU-GEI WP2 Study

Objectives: To establish whether the risk of psychotic disorders in cannabis users changes with time following cannabis cessation using data from the European Network of National Networks studying Gene–Environment Interactions in Schizophrenia (EU-GEI) case–control study. Methods: The EU-GEI case–control study collected data from first episode psychosis patients and population controls across sites in Europe and Brazil between May 2010 and April 2015. Adjusted logistic regressions were applied to examine whether the odd of psychosis case status changed: (1) with time following cannabis cessation and (2) across different cannabis use groups. Results: Psychosis risk declined following cessation of cannabis use (β = −0.002; 95% CI −0.004 to 0.000; P = 0.067). When accounting for duration of use, this effect remained (β = −0.003; 95% CI −0.005 to −0.001; P = 0.013). However, in models adjusting for frequency and potency of use the result was not significant. Analysis of different cannabis use groups indicated that ex-users who stopped 1 to 4 weeks previously had the highest risk for psychotic disorder compared to never users (OR = 6.89; 95% CI 3.91–12.14; P < 0.001); risk declined for those who stopped 5 to 12 weeks previously (OR = 2.70; 95% CI 1.73–4.21; P < 0.001) and 13 to 36 weeks previously (OR = 1.53; 95% CI 1.00–2.33; P = 0.050). Ex-users who stopped 37 to 96 weeks (OR = 1.01; 95% CI 0.66–1.57; P = 0.949), 97 to 180 weeks (OR = 0.73; 95% CI 0.45–1.19; P = 0.204), and 181 weeks previously or more (OR = 1.18; 95% CI 0.76–1.83; P = 0.456) had similar psychosis risk to those who had never-used cannabis. Conclusion: Risk of psychotic disorder appears to decline with time following cannabis cessation, receding to that of those who have never used cannabis after 37 weeks or more of abstinence. Although, preliminary results suggest that frequent users of high potency types of cannabis might maintain an elevated risk compared to never users even when abstaining for longer than 181 weeks.