Doubt that cop’s boy corrupted file after consuming drug (9)
I believe the answer is:
disbelief
'doubt' is the definition.
(disbelief is a kind of doubt)
'cop's boy corrupted file after consuming drug' is the wordplay.
'cop's' becomes 'dis' (detective inspector).
'boy' becomes 'b' (abbreviation used in schools).
'corrupted' indicates an anagram.
'after consuming' means one lot of letters goes inside another.
'drug' becomes 'e' (e is another name for ecstasy).
'file' is an anagram of 'elif'.
'elif' enclosing 'e' is 'elief'.
'dis'+'b'+'elief'='DISBELIEF'
'that' acts as a link.
(Other definitions for disbelief that I've seen before include "having exhausted trust fund?" , "Incredulity" , "Refusal to advance credit" , "Lack of faith" .)