an answer the cocaine v alcohol question -- never had I the feel, once the 'buzz' of a drink was wearing off, that I REALLY wanted another drink. cocaine does it to me everytime, and I just happen to have what it takes to say, what I had was enough, that was fun, and now back to the world without cocaine.
I think your grounding in the world of chemicals your body can produce has a lot to do with it. if you are trying to escape your own chemical world, into someone or something else's chemical world, then that place becomes home to you, and yourself becomes this place you are trying to leave. If you don't want to simply visit these other worlds, and come back to your own world when you are done, then, I guess, this could be the chemical and spiritual root of addiction, not being okay in your own emotional and chemical 'cloud' becoming dependent on constant injections into your cloud.
perhaps there is something to the anal-retentive need for order, and how first usages of many chemicals do appear to bring order to the world, as it's signal so overwhelmingly tunes out the other influences of the noosphere.