This seems unlikely. There exists a strong correlation because schizophrenia develops during puberty and self medication is normally an attempt to cope. Likewise, puberty is usually the first time one can gain access to pot. Pot is the biggest drug used to self medicate. Pot didn't cause the schizophrenia. Yet it strongly correlates. There might exist causality of pot on brain development and schizophrenia, as it's known pot hinders brain development during and before puberty. As such, it may well cause more severe schizophrenia. But that's supposition on my part and afaik, unfounded.