City of London to stop importing second drug (7)
I believe the answer is:
ecstasy
'drug' is the definition.
(ecstasy is a kind of drug)
'city of london to stop importing second' is the wordplay.
'city of london' becomes 'ec' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to stop' becomes 'stay' (synonyms).
'importing' indicates putting letters inside.
'second' becomes 's' (common abbreviation).
'stay' placed around 's' is 'stasy'.
'ec'+'stasy'='ECSTASY'
Can you help me to learn more?
(Other definitions for ecstasy that I've seen before include "Powerful hallucinatory drug" , "Intense happiness" , "Street name for the MDMA drug" , "Rapture; drug" , "State of euphoria and drug that induces it" .)