They ended up figuring in significantly in last weeks game. We went back to talk to an NPC, a drow sorcerer, we were working with to find him acting really strange. We made jokes about him being stoned and I even asked to make a "smell check" and was indeed an opium addict. While getting frustrated with his behavior, one of the PCs started pushing him around and ended up ripping off his necklace. Turns out that he was in the service to another demon and hiding from Lolth and the necklace was the only thing preventing her from finding him. Once ripped off, he freaked, but being too stoned to convey why, we couldn't help (plus, he was attacking us) and a giant spider arrived and carried him away.
Moral of the story: recreational drugs can kill.