I know this is bumping an old thread but please, do not compare quetiapine to diazepam, this is very, VERY dangerous. And do not be confused, quetiapine definitely DOES cause a withdrawal syndrome, it’s very unpleasant. Tremors, hallucinations and anxiety are just the tip of the iceberg so to speak.
Taking quetiapine without a prescription or a valid psychiatric reason is quite dangerous and can cause rebound psychosis. Also, while you are correct about the addictive nature of benzodiazepines, you are extremely incorrect to assume that quetiapine is in any way “safer” to take on a daily basis than diazepam; there isn’t even enough known about quetiapine to make that claim, as it’s a fairly new (as far as drugs go) chemical, and not much is known about its long term affects.
To answer the question, you will likely need to skip your seroquel the night of (or day, if you take it in the morning), and depending on how long you’ve been taking it daily, I’d say take a slightly larger dose of mushroom than usual, because it is likely that the quetiapine left over in your system will lessen the desired effect of the mushroom. I can say from experience that this is quite unpleasant, because you’re still going to feel physically like you’ve taken mushrooms, in the sense that you will definitely still feel a lot of the “body stone”, as well as likely not sleeping and having obnoxiously rapid and hard to follow thought patterns like you’re tripping, but none of the pleasant visuals or feelings of being “connected” either with nature or other people..you’ll kinda just feel..weird, and a little sick.
TLDR, do not take quetiapine the day of the trip, consider using a higher dose, do not take quetiapine without a prescription or a reason and do not let yourself believe that something with very little human research is safer than something they’ve been studying the effects of for many years and is on the WHO list of necessary drugs.