My relative had mental breakdown and was forced to go to the psychiatric hospital. After few years it repeated because he stopped taking his prescribed pills and now he does not want to go there himself, logical reasoning does not work at all. It's a terrible situation, calling medics and forcing person to go to the hospital does not sound like a good idea, because he'll hate you for that and keeping it unchecked might do no good either. Neuroleptics are not harmless, they make person very slow and apathetic, they kill all feels, that's why some people want to stop taking them. I can't imagine anything worse than mental illness.
My wife has a school friend who is schizophrenic. She tried - hard - to get her some help, but "getting help" maps onto "suppressing what reality I think I can perceive" really fast. Her friend was already terrified of Tibetan spies infiltrating her family, and just figured they got to my wife, too.
It would be nice to hear any strategies that do work. In the end, we couldn't find any.