cold fjord writes: State level marijuana legalization efforts across the U.S. have been gaining traction driven by the folk wisdom that marijuana is both a harmless recreational drug and a useful medical treatment for many aliments. However, some cracks have appeared in that story with indications that marijuana use is associated with the development of mental disorders and the long-term blunting of the brain's reward system of dopamine levels. A new study has found that marijuana appears to have a widespread effect on blood flow in the brain. EurekAlert reports: "Published in the Journal of Alzheimer's Disease, researchers using single photon emission computed tomography (SPECT), a sophisticated imaging study that evaluates blood flow and activity patterns, demonstrated abnormally low blood flow in virtually every area of the brain studies in nearly 1,000 marijuana users compared to healthy controls, including areas known to be affected by Alzheimer's pathology such as the hippocampus. According to Daniel Amen, M.D., 'Our research demonstrates that marijuana can have significant negative effects on brain function. The media has given the general impression that marijuana is a safe recreational drug, this research directly challenges that notion. In another new study just released, researchers showed that marijuana use tripled the risk of psychosis. Caution is clearly in order.'"