Addict taken in because relapsed (4)
I believe the answer is:
user
'addict' is the definition.
(I've seen this before)
'taken in because relapsed' is the wordplay.
'taken in' says the answer is hidden in the clue.
'USER' can be found hidden inside 'because relapsed'.
(Other definitions for user that I've seen before include "Someone who exploits another" , "With 1a [NEW] he'll need different login" , "junkie" , "Right long-established" , "One taking advantage" .)