People claiming to be Christ get locked up, generally.

And since our mental health facilities are absolute shit, its usually handled by the penal system rather than medically.

That being said, if you want a true story, very interesting, but short read… Check out “The Three Christs of Ypsilanti”

It was written after an experiment to treat delusions, with the notion that talking with people with the same core delusion would effectively lead them to a logical conclusion that NONE of them were Christ.