Depends on where you are in the world. Try to get a doctor to him. He probably won't appreciate you intervening like this, but it's for the best.
Unpalatable as this may sound, his family will have had a huge influence over his life, and it's almost inconceivable that they didn't contribute to the state he's in. So, some family-based therapy in the longer-term may also yield good results.
I know this isn't probably what you want to hear, and most doctors wouldn't dare say it, but it's the way it often is, unfortunately. None of us exist in a social vacuum and we are all influenced by the behavior of those around us.
Good luck.