Objectives Despite the health risks and public harm associated with heavy drinking, tobacco and marijuana use, the abuse of these substances remains common among youth in Canada. In this paper, for these three substances we examine (a) changes in their use over time, (b) age of onset, (c) co-morbid use, and (d) sociodemographic factors associated with their use in a nationally representative sample of Canadian youth.

Methods Data were collected from students in grades 7 to 9 as part of the Canadian Youth Smoking Survey (n = 19,018 in 2002; n = 29,243 in 2004; n = 71,003 in 2006).

Results Alcohol is the most prevalent substance used by youth. Co-morbid substance use was common, and it was rare to find youth who had used marijuana or tobacco without also having tried alcohol. There were high rates of underage youth trying alcohol, as well as a high prevalence of binge drinking and co-morbid use with tobacco and/or marijuana. Onset of alcohol and tobacco occurred at younger ages than marijuana. School performance and disposable income were associated with increased risk of these three behaviours.

Conclusions The data suggest that alcohol, tobacco and marijuana are used by a substantial number of youth in Canada, despite age and legal regulations prohibiting their use. Considering the inter-relationship between alcohol and tobacco onset, future research should examine the potential impact that the increasing popularity of alcohol use may have on future youth smoking rates.