Changes in the transition from cannabis use to use disorder by decade of first use: Findings from the Australian National Mental Health and Wellbeing surveys.

Abstract

Background and aims: As cannabis becomes increasingly accessible and products more potent, it is critical that we understand how this may impact the risk of transitioning from cannabis use to cannabis use disorder (CUD). We aimed to examine whether the risk and speed of transition from cannabis use to CUD differ by decade of first cannabis use.

Method: Cross-sectional surveys. Data were drawn from the two most recent Australian National Surveys of Mental Health and Wellbeing (NSMHWB; age range: 16-85): 2007 (n = 8841) and 2020-22 (n = 15 893). Among participants who had ever used cannabis (n = 4731), the number of years from age of first use to age of first CUD onset were calculated, with those never experiencing a CUD censored at age of interview. Participants were then grouped by their decade of first cannabis use (<1980s; 1980s, 1990s, 2000s, ≥2010s). Survival analysis was performed to estimate the accumulative risk of CUD. Cox proportional hazards models examined whether decade of first use was associated with speed of progression from first use to first CUD while controlling for demographic, other substance use disorders (SUD), mental health disorders, and mental health service use.

Results: Across 1-, 5-, and 10-years following first use, the risk of developing CUD was consistently lowest among those who initiated before 1980 (cumulative risk [CR] = 0.07, 0.16, 0.18 respectively) and highest among those who initiated in the 1990s (CR = 0.12, 0.25, 0.28 respectively) and 2000s (CR = 0.13, 0.24, 0.26 respectively), although confidence intervals overlapped at earlier time points. After adjusting for demographics, other SUDs, mental health disorders, and mental health service use characteristics, those initiating cannabis use in the 1990s [HR = 1.47; 95% confidence interval (CI): 1.08-1.99], 2000s (HR 1.37; 95%CI 1.05-1.81) and 2010 ≥ (HR 1.70; 95%CI 1.13-2.56) exhibited statistically significantly elevated hazards of CUD relative to those first using cannabis prior to 1980.

Summary: The risk and speed of transitioning from first cannabis use to cannabis use disorder appears to be greatest in those individuals initiating use after 1980. This increased risk may be partially driven by more potent cannabis products and easier access, which has important implications for cannabis regulation and the design of early intervention.