Don't kick him out the door..... but tread lightly...... sounds like everyone around him is on thin ice.

A mental illness like sever bi-polar or schizophrenia is something that basically can take away everything if not properly medicated.   Even when medicated, like the previous guy said, and i would add 9.9 people out of 10 think they can eventually go off the medication.  And thats never good.

Watch the movie "A beautiful mind".......  and put yourself into the main character.

For sure do not assume your buddy has bipolar or any other mental disease.       If he is in his early to mid 20's, its possible the signs were there before that age, but came on strong now.......

Unfortunately, there is nothing you can do but be a friend, even when his mind is doing everything to make you want to do the opposite..... Thats the bitch of it.......  If it is mental illness, its a lifetime of patience.

PS:  keep him away from alcohol at all costs.