To evaluate the influence of potential confounds, group differences were examined in an ANCOVA (N = 72). Specifically, cigarettes smoked, FTND score, lifetime other drug use, and parental history of SUD were greater in MJ+ALC users than controls. ANCOVAs indicated that the group differences in FA and MD reported above persisted after controlling for these variables (F(12,54) = 6.50, P<0.001). Further, to see if parental SUD history might interact with adolescent substance use in accounting for variability in white mater integrity, follow-up hierarchical regressions (N = 72) entered parental SUD history on step 1, substance use group on step 2, and their interaction on step 3. Positive parental SUD history predicted lower FA in the right crus cerebri, but not other regions, across users and controls (β = -.37, P = 0.001), yet substance group status continued to predict FA above and beyond parental history (β = -.33, P = 0.003). The parent history × use group interaction did not predict FA.
