Initially relapsing, every heroin addict battles recovery (5)
I believe the answer is:
rehab
'recovery' is the definition.
(where a drug addict might recover)
'initially relapsing every heroin addict battles' is the wordplay.
'initially' suggests taking the first letters.
The initial letters of 'relapsing every heroin addict battles' is 'REHAB'.
(Other definitions for rehab that I've seen before include "getting dry?" , "Treatment for alcohol abuse" , "Treatment for alcohol or drug dependence" , "convalescent home?" , "brief convalescence?" .)