It does not cause schizophrenia, and its unclear whether it increases the risk or not. I doubt it would cause someone who would not otherwise develop it to do so. For people who react negatively to it I imagine it does not help matters..but yeah some of the correlation between schizophrenia and cannabis is just some people with schizophrenia smoke it as well as have the disorder....or might even self medicate with marijuana correlation does not always mean causation.