Drug user did wrong, breaking law (6)
I believe the answer is:
addict
'drug user' is the definition.
(addict is a kind of drug user)
'did wrong breaking law' is the wordplay.
'wrong' indicates anagramming the letters.
'breaking' indicates putting letters inside.
'law' becomes 'act' (I've seen this before).
'did' is an anagram of 'ddi'.
'ddi' going inside 'act' is 'ADDICT'.
(Other definitions for addict that I've seen before include "One who is dependent on something, alcohol say" , "Fanatic devotee" , "One unable to kick habit" , "Junkie, substance abuser" , "One hooked on something" .)