The study concluded that in the cases of substance abuse, overlapping expressions of CNR1 and DRD2 are the causes of CNR1-DRD2 interactions and that the various polymorphisms of CNR1 and DRD2 genes may play crucial roles in the nature of these interactions in terms of promoting or mitigating an individual’s cannabis addiction risk factor [34]. This evidence concerns the gene DRD2 and substance abuse.