Stop putting drug in box (5)
I believe the answer is:
cease
'stop' is the definition.
(synonyms)
'putting drug in box' is the wordplay.
'putting drug' becomes 'e' (I can't explain this - if you can you should believe this answer much more).
'in' is an insertion indicator.
'box' becomes 'case' (I've seen this in another clue).
'e' put within 'case' is 'CEASE'.
Can you help me to learn more?
(Other definitions for cease that I've seen before include "Political group" , "Desist" , "Finish, end" , "Stop, finish" , "Stop, terminate" .)