Police fire on pub which produces drug (9)
I believe the answer is:
ibuprofen
'produces drug' is the definition.
'ibuprofen' can be an answer for 'drug' (ibuprofen is a kind of drug). I'm not sure about the 'produces' bit.
'police fire on pub' is the wordplay.
'police' indicates anagramming the letters (police can mean to control or manage).
'fire'+'on'+'pub'='fireonpub'
'fireonpub' with letters rearranged gives 'IBUPROFEN'.
'which' is the link.
Can you help me to learn more?
(Other definitions for ibuprofen that I've seen before include "Painkiller" , "Drug" , "Anti-inflammatory medicine" , "anaesthetic" .)