Difficult prisoner loudly taking drugs (9)
I believe the answer is:
confusing
'difficult' is the definition.
'prisoner loudly taking drugs' is the wordplay.
'prisoner' becomes 'con' (abbreviation for 'convict').
'loudly' becomes 'f' (short for forte - 'loud' in music).
'taking drugs' becomes 'using' (I've seen this before).
'con'+'f'+'using'='CONFUSING'
(Other definitions for confusing that I've seen before include "Perplexing, puzzling" , "Bewildering or perplexing" , "Muddling" .)