A, Whole-brain voxel-based morphometry between marijuana users and control participants. Images are thresholded at z = 2.5. The most significant increases in gray matter density were in the left nucleus accumbens extending to the hypothalamus, sublenticular extended amygdala, and amygdala (Tables 2 and 3). B, Associations between gray matter density and drug use measures; p < 0.0125 was considered to be significant after correcting for 4 comparisons (Table 4). GMd, Gray matter density. C, Nucleus accumbens volume was increased in marijuana users and was associated with drug use measures. Error bars represent SE. An asterisk above the bar chart on left indicates that significance met p < 0.05 uncorrected (p = 0.037; Table 2), which was a trend effect after correcting multiple comparisons. The association with drug use, after correcting for 4 comparisons (p = 0.05/4, or 0.0125), was determined to be a trend toward significance (Table 4). CON, Controls; MJ, marijuana participants.