https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4604190/pdf/13311_2015_Article...Overall, it seems that high THC cannabis can worsen symptoms of schizophrenia and make them appear earlier in life. It does not seem that THC induces schizophrenia in those who are not prone to develop it eventually. CBD can be helpful in treating the symptoms of schizophrenia.
https://www.ncbi.nlm.nih.gov/pubmed/29241357