Schizophrenia is not an objectively determinable fact. There is no test for schizophrenia. It cannot be proved or disproved.

Schizophrenia is an attribution, like ugliness. Your are schizophrenic when a psychiatrist decides that you are schizophrenic. Claims that cannabis causes schizophrenia are politically correct and will ensure researchers funds, but they can have no scientific basis, because science deals with demonstrable facts, not attributions.

Of course cannabis is a psychoactive substance. That's why people use it. Like all psychoactive substances, there is risk involved in its use. If we want to eliminate risks, we should start by prohibiting automobiles. Many more people are killed or permanently maimed from automobiles than from cannabis (which doesn't kill anybody).