I came across this podcast featuring Dr. Gabor Mate. He has worked with some of the most severely affected addicts and I've learnt a lot from this interview. I strongly recommend listening to it. His explanation about addiction and how it begins is eye opening.
If you're very busy for the whole thing perhaps listening to it from 01:06:00 (from one our and sixth minute onwards) for the next 20 mins would be helpful too.