Cannabis use disorders and altered brain morphology: Where is the evidence?

Cannabis use disorders (CUDs) affect 13.1 million individuals worldwide. Brain morphology specific to CUDs may mediate the adverse behavioral outcomes of CUDs. We reviewed findings from 20 human neuroimaging studies on grey and white matter morphology in cannabis users that specifically included CUD assessments. There is evidence for CUD-specific morphological abnormalities within the striatum, medial temporal lobe, prefrontal cortex, cerebellum, and corpus callosum. Factors that may aggravate morphological abnormalities associated with CUDs include earlier onset age, higher lifetime exposure, and CUD-associated problems, while abstinence may result in (partial) recovery. These observations suggest that the neural substrates of compulsive cannabis use (e.g., striatum) may be distinct from those linked to cannabinoid exposure (e.g., hippocampus). The lack of studies examining individuals with a diagnosed CUD prevents drawing strong conclusions on CUD-specific morphological abnormalities. Comparing cannabis users with and without CUD is essential to delineate the neurobiology and inform new treatment strategies.