The identification of tobacco, alcohol and other drug involvement as factors associated with progression from opportunity to dependence suggests that a pattern of poly-use emerges. Although alcohol use has previously been found to be associated with early onset of cannabis use (Coffey et al., 2000) it was not associated with opportunity to use cannabis in the present analyses, which may partially reflect the high prevalence of monthly alcohol use in the current sample. The comparatively rarer outcomes of tobacco dependence, other drug use and other drug dependence were found to be associated with increased speed of progression to cannabis dependence. The use of both tobacco and cannabis has been frequently observed (Agrawal et al., 2012, 2010; Hindocha et al., 2015), and regular cigarette smokers are more likely to report earlier cannabis use opportunity (Agrawal et al., 2013). Present results strongly supported this finding, and extend it to show weekly tobacco use and dependence were significantly associated with speed of progression to cannabis dependence. The observed association between cannabis dependence and tobacco may be due to a number of factors including shared genetic and environmental influences, the co-administration of tobacco and cannabis, and smoking habituation (Agrawal et al., 2012).
