Age-period-cohort analysis of trends in tobacco smoking, cannabis use, and their co-use in the Australian population

Background and aim The prevalence of tobacco smoking has declined in most high-income countries, while cannabis use has been rising. Moreover, cannabis use has been found to have increased among cigarette smokers in recent years in jurisdictions where it has been either decriminalized or legalized. This study measured trends in cannabis, tobacco and the co-use of cannabis and tobacco in Australia. Design Age-period-cohort analysis. Setting and participants Participants were n = 143 344 individuals aged 18-80 years who participated in Australia's National Drug Strategy Household Surveys (NDSHS) between 2001 and 2019. Measurements Regular (weekly/more frequently): (1) tobacco smoking only, (2) cannabis use only and (3) the co-use of cannabis and tobacco. Findings Prevalence of only smoking tobacco decreased in all age groups (P < 0.001) and birth cohorts between 2001 and 2019, but the co-use of cannabis and tobacco did not. Younger cohorts were much less likely to co-use tobacco and cannabis (P = 0.02). Period trends showed that both cannabis use only and the co-use of cannabis and tobacco have increased since 2013. Conclusion There has been a consistent decrease in exclusive tobacco smoking across age, period and birth cohorts between 2001 and 2019 in Australia, although there is a recent increasing period trend in cannabis use with or without tobacco. The non-decreasing trend of co-use may reflect the strong tobacco control policies introduced over the period and changing attitudes towards cannabis use in Australia.

Automated summary

This study examined the trends in tobacco smoking, cannabis use, and co-use of cannabis and tobacco in Australia. The results showed a consistent decrease in exclusive tobacco smoking from 2001 to 2019, across various age groups, time periods, and birth cohorts. However, there was an increasing trend in cannabis use, with or without tobacco, since 2013. Younger cohorts were less likely to engage in co-use of tobacco and cannabis.