Not my business?

Hey Brooke,
My question to you is, if this is my business? I am pretty sure it is not, but since it is my son (grown or not) I am not sure how to proceed.
I believe he is using alcohol or marijuana to buffer and I am wondering if it is my business to ask him about the situation.
It is very difficult to have a relationship with him as he says he does not want to talk about it (most subjects) and as a mother I am unsure how to handle this.