Can "be on something" mean "you take drugs like marijuana or cocaine"? Why is it "on" for drugs?
smith- I know, but I'm not on anything. I work my ass off every day. I've been doing this since I was 5,
and everybody thinks thatI'm on something, but I'm not. I mean, we get tested.
Mel- Look. I'm not the steroid police.
smith- Well, isn't that why you've been following me around?
Yes, that is what it means, and it applies to drugs both legal and illegal.
As to why we use "on" in this circumstance, I'm not truly sure. I'm not sure there's always great logic for any prepositional usage in any language, other than custom or habit. Perhaps it's a verbal shorthand for "on a course of X" which we would say when referring to legal drugs such as antibiotics, and has grown over time to refer to illegal drugs as well?
'On' is a very expressive little word, used in this sense. As an example of its cooloquial use I quote the conductor of my choir (referring to a particularly strange musical line at last week's rehearsal): 'What was Monteverdi on?'
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