Plaintiff's account about drug addict (7)
I believe the answer is:
accuser
'plaintiff's' is the definition.
(thesaurus)
'account about drug addict' is the wordplay.
'account' becomes 'ac'.
'about' becomes 'c' (abbreviation for 'circa').
'drug addict' becomes 'user' (I've seen this before).
'ac'+'c'+'user'='ACCUSER'
(Other definitions for accuser that I've seen before include "Person charging" , "Person making a charge" , "Search, rub, thoroughly" , "Prosecutor" , "one levelling the charges" .)