The reason
OxyContin became
popular for
recreational use is
accessibility. As
HongPong hinted at in his writeup, OxyContin first registered as a serious problem in places like eastern
Kentucky,
West Virginia and
southwestern Virginia. OxyContin users, as opposed to users of other illicit drugs, did not have to access underground
supply chains (in the case of
imported drugs) or grow it (
marijuana -- this is also a prime marijuana-growing region of the US). They could either
steal it from the local
pharmacy or simply get a complicit
doctor to prescribe it unnecessarily.
Combine this accessibility with the sad economic shape of the Appalachian region, and you had the rise of a new drug, which first became known widely as "the hillbilly heroin." It did not take much money or effort to get into this habit, and, as other WUs have mentioned, it's incredibly difficult to break.