@pta, getting as much information as possible is good, but I would encourage you to get legal advice. As his guardian you are responsible for his care, so if he is harmed or harms others, you may be held responsible. Just because he has not been violent before, doesn’t mean he can’t become that way without meds.

You describe him as psychotic. This would concern me and I don’t think I’d live with his decision to not take prescribed meds. If he refuses, I’d seek legal advice about transferring guardianship to another (perhaps the state or county) and having him relocated.
This may sound harsh, but I had a good friend who was seriously injured by her adult son who was diagnosed with schizophrenia.

Best of luck to you and your son.