Green’s Dictionary of Slang

(US drugs) oxycontin.

2001		ADS-L 26 Dec. 🌐 ‘“Hillbilly Heroin” should get some WOTY [i.e. word of the year] consideration, especially if you add a category of new drug terms. I didn’t spy it on the Wordspy.’ ‘I hope to hell it won’t, since it stigmatizes, once again, the Appalachian region. Oxycontin is indeed a scourge in this area, but West Virginia deserves better.’.
2001		Guardian (UK) 25 June 🌐 In his tiny home town, Justice, [...] four out of 10 young adults are hooked on a potent prescription painkiller called OxyContin. In this part of West Virginia, and the neighbouring hill counties of Virginia and Kentucky, they call it ‘hillbilly heroin’ or ‘poor man’s heroin.’ They also call it a plague.
2013		J. Stahl Happy Mutant Baby Pills 234: With the oxys it was all pleasantly incomprehensible. I forgot how hillbilly heroin made your ears ring.