Ironically, certain psychoactive substances like cannabis (high CBD and low THC) have been shown to be effective in the reduction of stress in schizophrenic people and doesn't contribute to psychosis even within families who have members with it. Interestingly, some use THC for their schizophrenia symptoms.
However, environmental factors (set and setting) can greatly increase the likelihood of onset of schizophrenia too.
On tulpamancy, I've heard of some (myself included) who "hear voices" but they're not the result of psychosis, but an internal dialogue and...
As someone who has an internal dialogue, hyperphantasia, and synesthesia, this sounds kinda risky to me. I'm all for imaginary friends (I'm 37 and still have mine), but putting this much work into creating a tulpa seems like a waste of time and frankly, kind of dangerous.
I've had times where the "voices in my head" have saved from suicide, but they weren't forced. They just came to me intuitively. If someone is consciously trying to create a "living entity in their mind" there's no telling what they could do with it if they had the mentality of malicious intent.