One thing I have been practicing since my daughter has been recovering is, I don't tell her what to do, how to do, or when to do. I will encourage her, I will support her, and I will love her.
I think encouragment is a big help to them no matter what. You might think it is falling on deaf ears, but I think some of the words of the wise do tend to stick.
There is a way of talking to them without enabling or trying to control. Choose your words wisely and you will feel comfortable with the way you are dealing with him. You can be there for him without enabling him.
My RAD always told me it meant so much to her when I didn't turn my back on her even when she was using. I didn't comply with what she wanted from me, but I didn't turn my back on her either.
Just be his mom and your instints will tell you what to say and not to say.
Hugs...............Lo