There's definitely been studies linking it to various mental health issues but they've always seemed to be the type of shit that falsely associates correlation with causation and with just a hint of the "reefer madness" hysteria as a driving factor. The potential for a selection bias on something like this is almost impossible to account for. Who's to say that every instance "confirming" a link isn't self-medicating?

I don't think there's anything to suggest an otherwise "normal" adult with no symptoms to suddenly develop schizophrenia if they start getting stoned all the time.

We also that people who've been diagnosed can still have episodes, regardless of medication and circumstance because it's not a condition that's easy to predict, control, or understand.