The New Orleans rap scene in the mid-90s had a heroin thing going on -- with some fixation on the joys of "laying that dope dick" (prolonged sex without ejaculating).
I don't remember which Hot Boy it was (BG?), but I read that when he came to New York in that period, the local name rappers were shocked that he casually asked them where to get some heroin. (I think he had a habit and it wasn't just for recreational dope-dicking, but I'm not sure.)
Blunts and 40s were in at the time, heroin had a bad rap (no pun intended) in NYC and most everywhere except NO. It already had the current stereotype of only appealing to white boys and old heads (though in fact, the big heroin cohort that started in 1965-75 was not so very old -- mostly in their 40s around 1995).
EDIT: And on topic, I predict (and would sort of like to see/hear) rappers get into GHB. To me, it makes sense in that scene somehow, more so than ketamine IMHO (no disrespect intended
@simstim lol). I'd also personally pick it over ketamine if only one of them could be popularized as more of a "street drug" in the US, as much as I'd like to see UK-style street ket here as well.