I concur that one of the most important things is for your son to stay clean and sober. Without that, it's impossible to separate the MI symptoms from the drug-induced ones. I would encourage him to become involved with a local AA or NA group, and there will be people there who can help keep him on that path.

Keep working with the doctors, and don't give up on him. By far one of the most helpful things is to have supportive people in his life who love him no matter what - even if he slips back into drug use. As his parent I know you're one of those.There is a light at the end of the tunnel.

The suggestion to get counseling for yourself is a good one. Being here on this forum is a decent place for support, but we're no replacement for a competent therapist.