Heavy overdose by heartless guy on street (6)
I believe the answer is:
stodgy
'heavy' is the definition.
(thesaurus)
'overdose by heartless guy on street' is the wordplay.
'overdose' becomes 'od' ('o.d.' can be a synonym of 'overdose').
'by' is a charade indicator (letters next to each other).
'heartless' means to remove the middle letters.
'on' is a charade indicator (letters next to each other).
'street' becomes 'st' (**).
'guy' with its middle removed is 'gy'.
'od' next to 'gy' is 'odgy'.
'odgy' put after 'st' is 'STODGY'.
(Other definitions for stodgy that I've seen before include "Heavy, starchy and hard to digest" , "Indigestibly heavy" , "Like heavy and filling food" , "Dull and heavy" , "Heavy to eat" .)