Remember dukie from the wire. He would be one such example. Functional parents, addicts, but functional. Not living on the streets.
Although she dropped her opposition years later after his mother improved, I still wouldn't hold his mother out as an example of a functional addict.
(Also when he was a child, didn't his mother send him to live with his grandparents because she was too dysfunctional to care for him? Or did I get that wrong?)