Factors associated with the timing and onset of cannabis use and cannabis use disorder: results from the 2007 Australian National Survey of Mental Health and Well-Being.

INTRODUCTION AND AIMS: To investigate the predictors of both initiation of cannabis use and transition to cannabis use disorder (CUD) in a nationally representative sample using discrete-time survival analyses.

DESIGN AND METHODS: Data from a nationally representative sample of 6935 Australian adults. Retrospective data on age of first cannabis use and onset of CUD were used to construct pseudo-longitudinal datasets and survival models used to evaluate factors associated with age of first use and time from first use to onset of CUD.

RESULTS: The oldest cohort (born 1942-1951) had lower cannabis use than younger cohorts, with first use also occurring at an older age. Multivariable discrete-time survival models showed other substance use, tobacco and alcohol use at very young ages, and mental disorders were associated with increased risk of cannabis use. There were 7.5% of those <65 years old at interview who had a lifetime CUD; mean time from first use to the onset of CUD was 3.3 years, with 90% of cases within eight years. Younger age of initiation and other substance use were strong predictors of the transition from use to CUD. Women with depression were more likely to develop a CUD; social phobia and panic disorder were also associated with transition from cannabis use to CUD.

DISCUSSION AND CONCLUSIONS: Patterns of cannabis use differ across birth cohorts. There are multiple factors associated with use and transition to CUD, with other substance use a strong predictor. Mental disorders also predict initiation and progression to CUD.