Drug reduced -- that could be a blow (8)
I believe the answer is:
uppercut
'a blow' is the definition.
(uppercut is a kind of blow)
'drug reduced' is the wordplay.
'drug' becomes 'upper' (a type of stimulating drug).
'reduced' becomes 'cut' ('cut' can be similar in meaning to 'reduced').
'upper'+'cut'='UPPERCUT'
'that could be' is the link.
(Other definitions for uppercut that I've seen before include "Swinging blow directed at an opponent's chin" , "Boxer's blow" , "Swinging blow from below aimed at an opponent's chin" , "one must take it on the chin" , "Swinging blow in boxing" .)