I may be mistaken, but I believe this is considered risen to the level of “first degree” because the death was a result of the commission of another crime, here, illegal drug use.
I could be wrong.
I could be wrong, but I don’t think drug use, as such, is a crime, at least in most states. Possession is a crime, and sale is a more serious crime.
Of course, it’s pretty difficult to use drugs without being in possession, so very possibly I’m just digging away at a nit here. :)