“…Adolescence is a high risk period for drug use, particularly alcohol, tobacco and marijuana (AIHW, 2008b;de Looze et al, 2011;Palmer et al, 2009), and the risks associated with the use of these substances is well established (Booth et al, 2010;Department of Health and Human Services, 2004;Ellickson, Tucker, & Klein, 2003;Hall & Solowij, 1998;Swahn, Simon, Hammig, & Guerrero, 2004). Despite evidence that the use of one drug increases the probability of use of other types of drugs (Fergusson, Boden, & Horwood, 2008;Korhonen et al, 2008;van Leeuwen et al, 2011), comparatively little research has examined the prevalence rates of adolescent multiple drug use (broadly defined as the use of two or more drugs either within a given time period).…”