Thanks guys! Not sure I actually want to salvage that friendship.
Zx... M is not an addict, but she does them occasionally which is why I told her no drugs and didn't worry about it. She has no apparent trouble not taking drugs whenever she wants. Though, if she keeps up I can definitely see her headed down that path. It seems fair to say Z is addicted to the pills, which M provides, and M is addicted to Z.
She told me she did not have any pills on her, which was obviously incorrect. Z rarely has drugs on him because M doles them out 3 or 4 at a time to him. If she handed him a full bottle she wouldn't see him for a week or so until he wanted more so she only gives him a few at a time so she can ensure he has to be "friends" with her. I kinda started to suspect she might have offered him pills when he agreed to come over, but I always prefer to wait for the evidence before getting mad at someone.
I dunno about bringing drugs everywhere though. I usually left mine at home and did them before I went somewhere and/or when I got home. Who wants to get pulled over with Class 1 narcotics in your car?