very early initiation of cannabis use, and such early cannabis use has been consistently and strongly associated with drinking initiation (Trim et al. 2010) and with development of alcohol and other substance use disorders (Lynskey et al. 2003, Grant et al., 2010). This finding may not be surprising in light of the strong comorbidity between cannabis and alcohol use disorders (Stinson et al. 2005) and of the genetic overlap between both use of and dependence on the two drugs (Sartor et al. 2010). Early cannabis use may also facilitate use of and problems with alcohol via engagement in other developmentally precocious activities (e.g. early sexual debut) and via delinquent peer affiliations, although the latter did not explain the association observed here. While the present study design cannot disentangle causal and correlative influences, and also did not account for the role of heavier cannabis involvement like frequent or problem use, it underscores the importance of considering cannabis initiation as a potent risk factor for drinking trajectories, a concern that is amplified by the growing legalization of recreational cannabis use in the U. S. and steadily decreasing rates of youth disapproval of regular cannabis use. (Pacek et al., 2015; Wilkinson et al.,
