An Australian research team has linked long-term, heavy cannabis use with structural brain abnormalities in humans. Fifteen long-term (more than ten years), heavy (more than five joints daily) cannabis-using men (mean age 40) with no history of polydrug abuse or neurologic/mental disorder were compared with 16 matched non-using control subjects. MRI imaging was used to measure the volume of the hippocampus and amygdala in the subjects. Investigators found both brain regions to be smaller in heavy cannabis users, with average volume reductions of 12% in the hippocampus and 7.1% in the amygdala. Cannabis use was also associated with subthreshold symptoms of psychotic disorders. The authors conclude that their findings are consistent with the view that cannabis use increases the risk of psychotic symptoms. (Regional brain abnormalities associated with long-term heavy cannabis use. Arch Gen Psychiatry. 2008 Jun;65(6):694-701).