Lil Wayne didn't help matters by using his time at the top to constantly remind everyone that he was blasted on Rx codeine-filled cough syrup all day every day. All the rappers we see now grew up in the era of Wayne. He was probably the first big rap "star" most of them knew about. I know this goes against my common assertion that Kanye is the most influential dude in the scene — but Kanye's appeal was always more universal, not at all confined to or even affiliated with "hood" scenes, while Wayne had ab entirely different vibe.
Anyway. Yeah, I imagine most of these folks are not anything approaching clean. Even the most sober-minded references xannies and shit. Then there's Future, basically marketing mass indescriminate consumption of everything, all the time, everywhere.
Personally I think opiates and benzodiazepines are more prevalent in thais culture than cocaine at the moment. Which scares me, because it's starting to spread and affect legislation for millions of people who take these mediations legally and responsibly (yah yah, I know ... hah hah, but they're out there.)