Tranquillising drug, one taken with hesitation after work (5)
I believe the answer is:
opium
'tranquillising drug' is the definition.
(opium might put you in a trance)
'one taken with hesitation after work' is the wordplay.
'one' becomes 'i' (Roman numeral).
'taken with' says to put letters next to each other.
'hesitation' becomes 'um' (um is said in hesitation).
'after' is a charade indicator (letters next to each other).
'work' becomes 'op' (common abbreviation for 'opus').
'i' put next to 'um' is 'ium'.
'ium' put after 'op' is 'OPIUM'.
(Other definitions for opium that I've seen before include "Addictive drug made from poppies" , "Derivative of Poppy" , "De Quincey confessed to eating it" , "wars with China" , "Narcotic derived from poppies" .)