Not working — had to slow consumption in the end (4)
I believe the answer is:
down
'not working' is the definition.
(down can mean broken or not working)
'had to slow consumption in the end' is the wordplay.
'in the end' suggests the final letters.
The last letters of 'had to slow consumption' are 'DOWN'.
(Other definitions for down that I've seen before include "Depressed - drink" , "Blue" , "Pillow filler - dejected" , "like the other set of clues" , "Out of sorts" .)