“…An early onset of use of a specific substance is a risk factor for disorders related to that substance (Behrendt, Wittchen, Hofler, Lieb, & Beesdo, 2009;Dawson, Goldstein, Chou, Ruan, & Grant, 2008;Grucza, Norberg, Bucholz, & Bierut, 2008;Pitkanen, Lyyra, & Pulkkinen, 2005), although this effect has not been proved across substance classes. In contrast, a younger age at first alcohol use has been associated with increased risk of cannabis use (Behrendt et al, 2012).…”