Gary Chan
G.C.K. Chan1, D. Becker2, P. Butterworth3, L. Hines4, C. Coffey2, W. Hall1, G. Patton2. 1Centre for Youth Substance Abuse Research, The University of Queensland, Australia; 2Centre for Adolescent Health, Murdoch Children’s Research Institute, Australia; 3Research School of Population Health, Australian National University, Canberra, Australia; 4Population Health Sciences Institute, University of Bristol, United Kingdom
Background: This paper (1) compares consequences of cannabis use initiated after high school with those of cannabis initiation in early adolescence, and (2) estimates the proportion of adverse consequences accounted for by adult onset and adolescent onset cannabis users.
Method: Ten-wave longitudinal study with 10 waves following participants from age 15 to 35 in Victoria, Australia (N = 1792). Key independent variable was patterns of cannabis use across 20 years, derived from self-reported frequency of cannabis use. The key outcome measures at age 35 were alcohol use, smoking, illicit drug use, relationship status, financial hardship, depression, anxiety and employment status.
Findings: Substantially more participants (13.6%) initiated regular use after high school (adult onset) than in adolescence (7.7%, adolescent onset). Most participants were in a minimal/ non-use group (63.5%) and a small proportion use cannabis occasionally throughout adolescence and young adulthood (7.7%). By the mid-30s, both adult and adolescent onset regular users were more likely than minimal users to have used other illicit drugs (OR > 20.4), be a high risk alcohol drinker (OR > 3.7), smoked daily (OR > 7.2) and less likely to be in relationships (OR < 0.4). Given that the prevalence of the adult onset group was nearly double of the adolescent onset group, the adult onset group accounted for a higher proportion of adverse consequences in the population than the adolescent onset group.
Conclusion: Cannabis users who began regular use in their teens had poorer later life outcomes than non-using peers. More surprisingly, the larger group who began regular cannabis use after leaving school accounted for most cannabis-related harms in adulthood, challenging the idea that late onset regular cannabis use is relatively benign.