I don't believe there's a causative link between weed and schizophrenia. What I do think is that perhaps people with developing schizophrenia or active schizophrenia may tend to self-medicate at a higher level than others, which could account for the link between schizophrenics and grass use. That is, they feel the disorientation and disorganized thoughts coming on and try to change that with weed and other substances. We know this is true for folks with bipolar disorder, who use psychoactive drugs and alcohol at a much higher rate, often for years, before they're officially diagnosed with bipolar disorder.