Amongst this existing evidence, there is little research examining the timing of opportunity to use cannabis. The study of transitions, and the timing of these transitions, can provide unique insights into influences on substance use (Behrendt et al., 2012; Hines et al., 2015b; Sartor et al., 2009, 2008), but only a limited number of factors have been studied in relation to speed of transition to cannabis use opportunity (with earlier opportunity representing a faster transition) These have focussed on early childhood behaviours, with disruptive behaviour early in school in males and better reading scores in females associated with earlier cannabis use opportunity (Storr et al., 2011). Similarly, no research to date has explored whether there is overlap between factors associated with earlier opportunity and those associated with the speed of progression to dependence. These include other substance use (Behrendt et al., 2009), some mental health factors (Behrendt et al., 2011) and gender (Ridenour et al., 2006; Wittchen et al., 2008). Exploring speed of transition to cannabis opportunity will determine whether risk factors for dependence are already exerting influence on drug
