there are several theories on the cause of Schizophrenia...
My step daughter has it and we think it was caused by a virus...but weed had nothing to do with it. That is just more BS propaganda...

http://www.schizophrenia.sk.ca/causes.htm

Taken in small doses, cannabis is a very safe sedative for most people, probably including some people with mental illness. But consider the "set and setting" of marijuana under marijuana prohibition. Obviously, it is difficult in California and impossible elsewhere in the world -- with the partial exception of Holland, another topic â?? for a doctor even to discuss the medical use of cannabis with anyone who is mentally ill. Patients may even be told that marijuana is a very dangerous drug. They will certainly be arrested and placed under even greater stress if caught using it. However, what if they use it, and find that it helps them? Is this good? Remember we are talking about someone who is mentally ill finding out that something that is anathematized actually helps them. That sort of thing could drive you crazy.

The point is that while some of the psychotic episodes associated with marijuana use may be caused by the marijuana and others may simply be correlated to failed self-medication, it is also worth considering that the set and setting of marijuana prohibition help create these conditions.

I agree with what Richard Cowans says: some of the marijuana related psychotic episodes might actually be iatrogenic â?? caused by the medical profession.
Many people with mental problems are on so many other drugs it would be impossible to tell what caused certain episodes...they are once again screaming reefer madness.