Matthew Large, MBBS, Senior Lecturer at the University of New South Wales, et. al, wrote the following in their Feb. 7, 2011 article titled "Cannabis Use and Earlier Onset of Psychosis: A Systematic Meta-analysis," published in the Archives of General Psychiatry:

“The results of meta-analysis provide evidence for a relationship between cannabis use and earlier onset of psychotic illness, and they support the hypothesis that cannabis use plays a causal role in the development of psychosis in some patients. The results suggest the need for renewed warnings about the potentially harmful effects of cannabis.”

Feb. 7, 2011