Ceasing cannabis use during the peak period of experimentation: A prospective study of the substance use and mental health outcomes of young adult cannabis users and former users

This is a copy of the presentation made by Dr Edmund Silins at the 2015 NDARC Annual Research Symposium in Breakout Session Two - Mental health, substance use and young people.

Background: Little is known about the impact of ceasing cannabis use during the peak period of experimentation. We investigated the association between cannabis use status (former, occasional, and regular use) at age 23 years and substance use and mental health outcomes at age 27 years.

Methods: Data were reported from the 20+ year cohort of the PATH Through Life Study, an Australian longitudinal study of young adults. Lifetime cannabis users (N=1410) at age 23 years were classified as former/occasional/regular users. Multivariable logistic regression was used to estimate the association between cannabis use status at age 23 years and six outcomes assessed at age 27 years.

Results: Compared to occasional cannabis users: (i) former users had odds of subsequent tobacco use (OR=0.67, 95%CI:0.52-0.85), illicit drug use (cannabis, OR=0.22, 95%CI:0.17-0.28; other illicit drugs, OR=0.29, 95%CI:0.22-0.39) and mental health impairment (OR=0.71, 95%CI:0.55-0.92) that were 29-78% lower; and, (ii) regular users had odds of subsequent frequent alcohol use (OR=2.34, 95%CI:0.67-1.34), tobacco use (OR=3.67, 95%CI:2.54-5.30), cannabis use (OR=11.73, 95%CI: 6.81-20.21) and dependence symptoms (OR=12.60, 95%CI: 8.38-18.94), and other illicit drug use (OR=2.95, 95%CI: 2.07-4.21) that were 2-13 times greater. Associations attenuated after adjustment but most remained significant.

Conclusions: Ceasing cannabis use during the peak period of experimentation is associated with reductions in substance use and mental health impairment even when compared to infrequent use. Whereas regular cannabis use in young adulthood is associated with subsequent increases in licit and illicit drug use. Findings support interventions that actively target young adult cannabis users during this period.