No legal responsibillities? techinically yeah, since the action alone is ILLEGAL, so anything beyond that is pointless, like whether or not to tell them "this is good shit."
But, are they responsible? I think they are, morally. And since our laws are derived from morality... hence ILLEGAL...
I see where you are coming from, though. Our drug laws are what created drug dealers in the first place, but does that excuse individual actions?... no.
So, if you sell something to someone you KNOW will hurt them, you're not responsible at all for it, because THEY wanted it?
If you ever open a pharmaceutical company, or any other company that sells consumable products (or products in general) .... I think I'll have to pass on buying anything from it.