On the flip side I've known people who were in therapy for long periods of time who kept abusing drugs, and it really got in the way of their dealing with any other issues.

I totally believe that this happens lots, but I can honestly say I have never seen it in my context. It's probably partly about class -- if you're homeless or very poor, all the system can see is ADDICT, and you have no chance of accessing therapy privately. Double all this if you're a person of colour.