Stops doing more acid to provide impetus (4-7)

I believe the answer is:

kick-starter

'impetus' is the definition.
(both can mean a cause or trigger)

'stops doing more acid' is the wordplay.
'stops doing' becomes 'kicks' (as in kicking a drug habit).
'more acid' becomes 'tarter' (tart can mean acid or sour).
'kicks'+'tarter'='KICK-STARTER'

'to provide' acts as a link.

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