P-88.00 SUBCORTICAL BRAIN ABNORMALITIES IN HEAVY LONG-TERM CANNABIS USERS REVEALED BY VOXEL-BASED MORPHOMETRY Objectives

Cannabis is the most widely used illicit drug worldwide, it being estimated that between 2.8 % and 4.5 % of the general population have used it, especially young people. Growing concern about potential effects of cannabis on cognitive function and the brain has led to an increasing number of neuroimaging studies being carried out on cannabis users1. Few of these have investigated the brain consequences of chronic, heavy use, however. In the present study we examined a sample of heavy long-term cannabis users without other substance abuse to determine whether long-term use is associated with brain structural changes. Material and methods The sample consisted of 14 long-term heavy cannabis users (mean duration: 14.3 years of regular use; mean use: 8.35 units/day) and 28 controls matched for sex, age and estimated IQ. Structural data were analyzed with FSL-VBM, an optimized voxel-based morphometry style analysis that yields a measure of differences in local grey matter (GM) normalized volumes. Group comparisons were carried out using a voxel-wise general linear model and permutation-based non-parametric testing, and using the cluster-based thresholding method. Results were corrected at a p-value of < 0.05 using family-wise error. Results The cannabis users showed increased GM volume in the basal ganglia compared to the controls (Figure 1). Thi