A pick-me-up leads to lack of stress (6)

I believe the answer is:

atonic

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'leads to lack of stress' is the definition.
I can't tell whether this defines the answer.

'a pick-me-up' is the wordplay.
'pick-me-up' becomes 'tonic' (I've seen this before).
'a'+'tonic'='ATONIC'

Can you help me to learn more?

(Other definitions for atonic that I've seen before include "(In poetry) unaccented" , "Unstressed (poetry)" .)

I've seen this clue in The Irish Times.

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