Correlations within the user group (n = 36) between FA values and alcohol and marijuana intensity, frequency, and duration were nonsignificant at P<0.004, but a few interesting trends emerged. Specifically, in three regions where users had lower FA than controls, FA was linked to use indices: right inferior frontal gyrus FA negatively correlated with years of regular drinking (r = -0.34, P = 0.04); but left SLF FA positively correlated with recent marijuana use days per month (r = 0.36 P = 0.03); and left occipito-frontal tract FA positively correlated with lifetime marijuana use (r = 0.39, P = 0.02), lifetime alcohol use (r = 0.38, p = 0.02), and years of regular drinking (r = 0.42, P = 0.01). In the left inferior longitudinal fasciculus, where users unexpectedly had lower MD than controls, lower MD related to more marijuana hits per month in the past 3 months (r = -0.35, P = 0.039) and fewer days since last alcohol use (r = 0.76, P = 0.03). For particularly heavy users (lifetime marijuana use ≥ 350 and lifetime alcohol drinks
