Both, I suppose. It comes down to why we have biology vs physics -- there are emergent phenomena that don't make sense to study only at the level of more reductive elements. Yes, chemistry is important in experience -- or taking chemicals wouldn't effect our experience. But we can clearly understand how an experience is psychologically damaging without haven't a clue as to its chemical underpinnings. And the point is that drug experiences can be damaging -- even if the drugs themselves are non-toxic.