Falls off the wagon
I believe the answer is:
relapses
'falls off the wagon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for relapses that I've seen before include "Deteriorates like pleasers" , "Regresses" , "becomes ill again" , "Backslides like pleasers" , "Falls back to former condition, perhaps of illness" .)