Let's go with the first assumption, that Mj is dangerous. ALL evidence from research methodologies designed to determine causality---which would require a longitudinal design to establish temporal precedence of brain harms attributable to MJ use; rather than alcohol abuse, whic stands as the single most frustrating, confounding variable in nearly every study claiming to have found a causative link between MJ use and harm to brain structures---found no differences between nonusers and daily users in the specific regions of interest [nucleus accumbens, amygdala, hippocampus, and the cerebellum--areas high in cannabis receptors]. Researchers found no evidence of differences in volumes b/t daily users and nonusers, adults or adolescents; however: alcohol consumption is associated with volume loss in the brain globally; even modest alcohol abuse may be associated with morphological changes and may represent an important confounding variable in studies on the effects of cannabis.