After work I took a narcotic (6)
I believe the answer is:
opiate
'a narcotic' is the definition.
(I know that opiate is a type of narcotic)
'after work i took' is the wordplay.
'after' says to put letters next to each other.
'work' becomes 'op' (common abbreviation for 'opus').
'took' becomes 'ate' (eating is a kind of taking).
'op' next to 'i' is 'opi'.
'opi'+'ate'='OPIATE'
(Other definitions for opiate that I've seen before include "Drug from poppies" , "Sedating drug" , "Drug inducing a false sense of contentment" , "A sedative drug" , "of heroin, perhaps" .)