NBC News (8/27, Fox) reports on two studies published in JAMA Psychiatry that examine the effect of marijuana on the brain. In the first study, which used MRI, investigators compared the brains of marijuana users to non-users. The results seemed to suggest that marijuana users “had some shrinkage in two brain regions called the amygdala and the right ventral striatum,” but when researchers compared marijuana users to their siblings, “the differences disappeared.” Meanwhile, a second study “found that marijuana appears to change the brain structure of young men with a high genetic risk of schizophrenia.”