Altered brain tissue composition in heavy marijuana users

Marijuana is the most widely used illicit substance in the United States: however. previous imaging studies have not detected altered brain structure in marijuana users compared to non-users. Voxel-based morphometry was used to investigate possible differences in brain tissue composition in a group of 11 heavy marijuana users and a group of 8 non-users. All participants were male. Statistical comparisons were made at the voxel level on T1-weighted magnetic resonance images to determine differences in gray matter and white matter tissue density Compared to non-users, marijuana users had lower gray matter density in a cluster of voxels in the right parahippocampal gyrus (P = 0.0001). and greater density bilaterally near the precentral gyrus and the right thalamus (P < 0.0-4). Marijuana users also had lower white matter density, in the left parietal lobe (P = 0.03), and higher density around the parahippocampal and fusiform gyri on the left side compared to non-users (P < 0.002). Longer duration of marijuana use (in years) was significantly correlated with higher white matter tissue density in the left precentral gyrus (P = 0.045). Our preliminary results suggest evidence of possible structural differences in the brain of heaxy marijuana users. and localize regions for further investigation of the effects of marijuana in the brain. (C) 2004 Elsevier Ireland Ltd. All rights reserved.