After work, I’m swallowing universal painkiller (5)
I believe the answer is:
opium
'painkiller' is the definition.
'after work i'm swallowing universal' is the wordplay.
'after' means one lot of letters go next to another.
'work' becomes 'op' (abbreviation for opus**).
'swallowing' is an insertion indicator.
'universal' becomes 'u'.
'im' enclosing 'u' is 'ium'.
'op'+'ium' is 'OPIUM'.
(Other definitions for opium that I've seen before include "De Quincey confessed to eating it" , "justification for war once?" , "Derivative of Poppy" , "Narcotic derived from poppies" , "Addictive drug made from poppies" .)