Quote Originally Posted by Oppositional P
I can think of a psychology text that states it clearly, but that's just one example. Usually insuflation is specified, but I still know examples that fit that bill
Well I don't know about your psych book but I found this within minuets of searching on google:

"At a certain point, c usage ceases to be a voluntary action: this is the onset of addiction. The positive reinforcement of the sensation of euphoria eventually alters the brain so that the use of c is obligatory"

Sounds like a physical addiction to me.

source:
The Neurobiology of Addiction