Hi,

Please do not let him use marijuana in any case. Marijuana can itself cause schizophrenia and significantly worsens the disease in those who already have it. The best you can do for him is to find a psychiatrist for him and make sure he gets back on medicines.

Best wishes.

The association between marijuana and schizophrenia is historically fraught. In the 1960s and 1970s, scientists thought that smoking weed could trigger psychosis in just about anyone. Today, these findings are more nuanced, but researchers still think that cannabis can trigger schizophrenia in people who are having family histories of the disorder. The resulting studies also suggest that people suffering from schizophrenia have increased risk for smoking pot.
My suggestion to you will be to convince your son to take medications for schizophrenia immediately and don't let him smoke much. Please go to the available psychiatric clinic and consult a doctor as soon as possible. God bless you.