Association between cannabis and psychiatric hospitalization.
To investigate the relationship between cannabis use and mental health. A cross-sectional analysis in a sample of 17 698 individuals with a mean age of 22 years (SD 4.2). Participants provided information on the amount and initial age of cannabis use and history of psychiatric hospitalizations through a web-based questionnaire. To quantify Δ(9) -tetrahydrocannabinol exposure, we operationalized cannabis use as the amount of money spent on cannabis per week over the last month. The odds ratio of having a history of psychiatric hospitalizations was the primary outcome measure. We found a dose-response relationship between the amount of cannabis use and the odds for psychiatric hospitalization. Adjusted odds ratios for hospitalization increased with the amount of cannabis consumed from 1.6 (95% CI 1.1-2.3) in incidental users to 6.2 (95% CI 4.3-8.9) in heavy users (>€25week). Our data suggested that concomitant drug use was an intermediate factor. Exposure to cannabis before the age of 12 years was found to carry a 4.8 (95% CI 2.9-7.8) times increased odds for past psychiatric hospitalizations. We conclude that early and heavy uses of cannabis are each and independently associated with poor mental health in its users.