An article in Live Science explores the links between marijuana and schizophrenia.  It offers the following

Marijuana abuse is common among sufferers of schizophrenia, the researchers say. In fact, other recent work has shown that the psychoactive ingredient of marijuana can induce some symptoms of schizophrenia in healthy volunteers, according to Matt Jones, a study researcher at the University of Bristol’s School of Physiology and Pharmacology. [Marijuana Worsens Schizophrenia]

(I want to state again that ignoring the possible bad effects of marijuana is just as foolish as the government ignoring the possible good effects.  If you use, read and be aware of some of the possible side effects.)