All I can tell you is what has and what has not worked for me and my daughter. I have had conversations with her about drugs and it has made me believe things will be better but ultimately she has had to want to. I know in my heart she replaces one drug with another because she cannot face the black mess in her head.
I have often written her letters which I just store. This gets the anger out of me for a moment. I will sometimes send her texts and they have variable responses. When I have a verbal conversation she has a reason or an excuse or a promise. Once in a while she talks about the issue with clarity but not enough to change the behaviour.
I am sorry but I cannot tell you what to do. I can say you can change you and your mind but not his which is what I’m trying to do. Hopefully my daughter and your son will do the same for themselves before it is too late.