Restraint gets Irene no end upset! (4)
I believe the answer is:
rein
'restraint' is the definition.
(I've seen this before)
'irene no end upset' is the wordplay.
'no end' means to remove the last letter.
'upset' is an anagram indicator.
'irene' with its final letter taken away is 'iren'.
'iren' with letters rearranged gives 'REIN'.
'gets' acts as a link.
(Other definitions for rein that I've seen before include "Hold back" , "(Horse's) guiding strap" , "Director's power" , "Slow-up" , "leading article?" .)