Smother husband in drug (5)
I believe the answer is:
choke
'smother' is the definition.
(thesaurus)
'husband in drug' is the wordplay.
'husband' becomes 'h' (abbreviation).
'in' indicates putting letters inside.
'drug' becomes 'coke' (cocaine).
'h' inserted within 'coke' is 'CHOKE'.
(Other definitions for choke that I've seen before include "Be unable to breathe" , "clog" , "Constrict the throat" , "Have difficulty breathing" , "cause congestion" .)