Shot in the arm, say (5)
I believe the answer is:
dosed
'shot in the arm say' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dosed that I've seen before include "Given a drug" , "Administered a portion of medicine to" , "Administered a drug to" , "Gave medicine to" , "Treated with medicine" .)