Kitty's drug (3)
I believe the answer is:
pot
I believe this clue is a double definition.
'kitty's' is the first definition.
(synonyms)
'drug' is the second definition.
(slang term for cannabis)
(Other definitions for pot that I've seen before include "Saucepan" , "Substance from the sap of trees" , "Container for 23" , "Cannabis - container - beer belly" , "Kitty; marijuana" .)