substantial co-occurrence of alcohol and other illicit drug use among individuals with marijuana abuse/dependence. Even though our study sample is representative of this population, comorbid alcohol and non-marijuana substance misuse remains as a potential confounding factor in genotype-phenotype associations despite inclusion of the former as a covariate in our statistical analyses. Further studies will need to investigate marijuana abuse/dependent patients without other comorbid substance misuse in order to more definitively assess gene-marijuana interactive effects on brain morphology and cognition.
