In a large meta-analysis, the connection between pot smoking and later development of psychotic disorders, including schizophrenia, was explored. The finding of an association does not mean that pot-smoking has a causative effect, since a correlational finding does not prove causation. For further details about the finding, see the article by Nestor Lopez-Duran (2011) at the Child Psychology Research Blog at the following website.
Lopez-Duran, N. (2011) Pot use and early psychosis: Does smoking marijuana increase the risk for schizophrenia? Child Psychology Research Blog.