Does smoking weed cause schizophrenia?

No: However it could unmask a latent schizophrenic process. "weed" at times causes euphoria and some feelings of paranoia. Hallucinations are not unusual either. Both are components of schizophrenia. In the 70's IV sedative hypnotics were used if one suspected schizophrenia but it wasn't clear. It would at times unmask schizophrenia symptoms of paranoia & hallucinations. Ethically it isn't done now.

Yes: There is growing evidence that people who start to use marijuana at a young age (under 16) and who use it regularly during those years are at greater risk of developing schizophrenia in their lifetime.

Cause earlier onset: Research results seem to show that marijuana can start a person's schizophrenia sooner than if he did not use mj. A younger person (with a brain, neurotransmitters, and receptors not fully developed), especially with a family history of schizophrenia or psychosis, should know his family history and avoid experimenting with mj or other illegal drugs that might have a similar effect on his brain.

Marijuana: Can cause psychotic symptoms that are indistinguishable from schizophrenia.