Just because he was prescribed drugs does not meas that he was taking them. Part of the mental illness is the belief that one is perfectly fine.
It is more likely that it was the lack of medications that allowed this to happen, had this person been properly medicated his schizophrenia and paranoia would have been treated.
Anti psychotic medications have a good history of success when properly matched with the patient. Your attitude is limited and comes from an irrational distrust. My guess is that if you (or a loved one should really need Rx drugs, you will jump and be glad for the power of prescription drugs. As long as the drug is matched to the individual case, then they do work and do so remarkably well. You and Tom Cruise's should go on a tour.
It is a case of proper diagnostics not bad drugs, just bad prescriptions.