Prevalence, Associations and Comorbidity of Cannabis Use and Cannabis Use Disorders in the Australian National Mental Health Surveys From 2007 to 2020-22.

The prevalence of past 12-month cannabis use remained stable in Australia between 2007 and 2020-22.

• Prevalence was 6.7% (95% CI 6.0%, 7.3%) in 2007 and 6.7% (95% CI 6.2%, 7.1%) in 2020-22.
• Data were drawn from the two most recent Australian National Surveys of Mental Health and Wellbeing.
• The 2007 survey included n=8841 respondents and the 2020-22 survey included n=15,893 respondents, with age range 16-85.
• Logistic regression was used to examine associations and changes in strength of association over time.

The prevalence of cannabis use disorder (CUD) also remained stable between 2007 and 2020-22.

• CUD prevalence was 1.0% (95% CI 0.7%, 1.3%) in 2007 and 0.6% (95% CI 0.4%, 0.8%) in 2020-22.
• The confidence intervals for the two time points overlap substantially, indicating no statistically significant change.
• CUD was assessed in both survey waves using comparable diagnostic methods.

Several individual characteristics were significantly associated with cannabis use disorder, with odds ratios ranging from 3.26 to 78.00.

• Factors associated with CUD included younger age (16-25 years), male sex, cannabis initiation before age 18, recent polysubstance use, other substance and mental disorders, and having visited mental health services.
• The overall range of odds ratios for these associations was OR 3.26–78.00.
• These associations were identified using logistic regression across both survey waves.

The association between younger age (16-25 years) and cannabis use disorder was significantly stronger in 2020-22 compared to 2007.

• The interaction odds ratio for younger age and CUD comparing 2020-22 to 2007 was OR 2.39 (95% CI 1.20, 4.77).
• This suggests young people may now be more vulnerable to developing CUD than they were in 2007.
• The authors note this finding is consistent with concerns about increasingly potent cannabis products and more liberal cannabis policies.

The association between polysubstance use and cannabis use disorder was significantly weaker in 2020-22 compared to 2007.

• The interaction odds ratio for polysubstance use and CUD comparing 2020-22 to 2007 was OR 0.42 (95% CI 0.20, 0.91).
• This indicates that the relative contribution of polysubstance use to CUD risk diminished between the two survey periods.
• Despite this weaker association, polysubstance use remained a significant correlate of CUD in the overall analysis (OR range 3.26–78.00).

The study was conducted in the context of increasingly liberal cannabis policies and more potent cannabis products, motivating monitoring of use and harm rates.

• The authors highlight that as cannabis policies become more liberal and products increasingly potent, it is important to monitor changes in rates of cannabis use and those at risk of harm.
• The study used data from the largest national mental health survey in Australia.
• The two survey waves (2007 and 2020-22) allowed examination of temporal changes over approximately 13-15 years.