Coffey and Lynskey (22) have shown that the transition from cannabis initiation to harmful use is more likely in males for whom drug availability is a strong determinant. Although several papers have used CCC pathway analyses to model the association between drug initiation and drug abuse or dependence (3, 15, 17) none has included the obviously critical upstream risk factor of drug availability, nor decomposed the association into genetic and environmental components of variance. Therefore, in order to determine the importance of this upstream risk factor, this study will model the association between cannabis availability, initiation and measures of abuse as a three stage process.
