Without being able to give any researches i think, its just the exact same thing as with any other drug. Is everybody, who is using alcohol truly addicted? Not really, there are a lot of grades to this. Although there are drugs, which are making it very likely you getting addicted to it (nicotine, heroine), its not a must. Reasons and factors can be biologocal and genetical as well as sociological and psychological as far as i am aware. I think, whats very nasty about P is, once you are getting addicted, its very difficult to get off of it again. By my own experience i can say, that i found it easier to quit cigarettes (almost a package daily) than to stop P. A lot of other P users say similar things.