You must be broke being on such drugs (6)

I believe the answer is:

uppers

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'drugs' is the definition.
(upper is a kind of drug)

I cannot understand how the remainder of the clue works.

(Other definitions for uppers that I've seen before include "the poor are on?" , "Out of luck, one may be on these" , "The 25 [PENNILESS] are on these" , "Top parts of shoes" , "Drugs" .)

I've seen this clue in The Guardian.

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