For the study, researchers at the University of Colorado “examined brain morphology in a sample of adult daily marijuana users versus nonusers and a sample of adolescent daily users versus nonusers. ”
Researchers “acquired high-resolution MRI scans, and investigated group differences in gray matter using voxel-based morphometry, surface-based morphometry, and shape analysis in structures suggested to be associated with marijuana use, as follows: the nucleus accumbens, amygdala, hippocampus, and cerebellum.”
According to Kent Hutchison, a clinical neuroscientist at the University of Colorado, Boulder, and the study’s lead author, “No statistically significant differences were found between daily users and nonusers on volume or shape in the regions of interest. Effect sizes suggest that the failure to find differences was not due to a lack of statistical power, but rather was due to the lack of even a modest effect.” He continues; “In sum, the results indicate that, when carefully controlling for alcohol use, gender, age, and other variables, there is no association between marijuana use and standard volumetric or shape measurements of subcortical structures.