Quit drugs and start to sew on retirement (4)
I believe the answer is:
stop
'quit' is the definition.
(synonyms)
'drugs and start to sew on retirement' is the wordplay.
'drugs' becomes 'pot' (slang term for mariujana).
'and' means one lot of letters go next to another.
'start to' says to take the initial letters.
'on retirement' says the letters should be written in reverse (retire can mean to go back).
The first letter of 'sew' is 's'.
'pot'+'s'='pots'
'pots' backwards is 'STOP'.
(Other definitions for stop that I've seen before include "Cease, halt" , "Prevent - desist" , "break" , "port of call" , "cut out" .)