It makes one sick, withdrawing article in city (6)
I believe the answer is:
emetic
'it makes one sick' is the definition.
(I've seen this before)
'withdrawing article in city' is the wordplay.
'withdrawing' says the letters should be written in reverse.
'article' becomes 'item' (I've seen this before**).
'in' means one lot of letters goes inside another.
'city' becomes 'ec' (the City of London postcode).
'item' reversed gives 'meti'.
'meti' placed within 'ec' is 'EMETIC'.
(Other definitions for emetic that I've seen before include "Medicine causing vomiting" , "Nauseating" , "Vomiting inducer" , "Medicine to make you sick" , "Inducing vomiting" .)