Sounds like what we alcoholics (recovering) call swapping the witch for the *****. As long as he has some mind altering drug to take away the fear and pain involved in addiction he will continue to self-destruct and cause much pain to all around him. So until he gets to his rock bottom, and starts to ask for help, the best thing is to stay clear. Hope I don't sound negative about this, but he may well get worse before he gets better if at all.
And that will only happen if he decides to change and seek the help he needs. He may need to get into a detox before his mind clears at all.