@izzythepush,
In my mind, if someone needs to be kept off or away from drugs, there is an implied relationship, whether or not it exists, between the person and drugs that is not, I don't think, intimated if the person is told to just stay off or especially if they are told to stay away from drugs. The nuances between "off" and "away" do change in relation to the verb they're attached to.
In my response I at least alluded to the nuances I spoke of, and Max definitely talked about them, which is why I made that point.
Also, I think I agree with Layman. I don't see why to stay off something you must have been on it at some point. Wouldn't that mean to stay away from something you'd have to have been near it at some point?
Child: I've never been on drugs.
Parent: Good. Keep staying off them.
Can you really not stay off if you've never been on?