My MC is male, early thirties, and moderately fit. In the story, he's being unknowingly dosed by another character.
My question is what could be a possible cause for psychosis? He's bought a new apartment, and ever since he's lived there he's been hearing voices, feeling cold (which I think I'll have that due to the fact that the A. C. isn't working) and he begins to feel some paranoia. I want him to become convinced that his place is haunted by ghosts.
I read some people's experiences on drug-forums, and I was thinking either pure meth, amphetamines or LSD, but I don't how effective that would be. While I'm alright with a some side effects, I don't want him to realise that there's a completely unsupernatural reason that he's hearing things until further on in the story. Plus, I've read that substance psychosis normally happens to chronic users or after one large dose. Is there something milder?
I've googled substance psychosis, psychosis causes, auditory hallucinations, drugs that cause psychosis.