I have never been on a set where drugs were openly offered or encouraged. I'm sure that in most cases, the companies would not want the risk of any legal problems that this would bring upon them. Many a scene requires the girls to make video disclaimers stating that no-one has offered you drugs or alcahol during the scene.
If I were to be seriously offered any kind of drug, and I don't mean immodium, or advil, I would not be comfortable working with that kind of crew...

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