Even if I don't know you, I'm proud of you for taking these difficult steps. You'll win in the end, I'm sure of that.
I've two grown up girls, never had big problems with them concerning drugs or drinking, maybe because we always could talk openly and they knew we were always there for them when needed.
If you, like you said, haven't talked to your mom for 18 years, then take the first step, it can't go worser than it already has been, can it. You only will gain by it I'm sure. Maybe your Mom is as frightened as you are, but equally desperately wanting to talk to you. You'll never know until you try.
Keep in touch with your bluepaged family here, they'll support you whenever you need supporting, day and night, because we're global (if that's a right word) there's always someone awake somewhere. Knock on our doors and we'll listen.
Like scattered leaves...my words will flow