Die by essentially persisting with heroin (6)
I believe the answer is:
perish
'die' is the definition.
('perish' can be a synonym of 'die')
'by essentially persisting with heroin' is the wordplay.
'by' becomes 'per' (**).
'essentially' says to take the centre.
'with' is a charade indicator (letters next to each other).
'heroin' becomes 'h' ('H' can be a synonym of 'heroin').
The middle of 'persisting' is 'is'.
'per'+'is'+'h'='PERISH'
(Other definitions for perish that I've seen before include "Expire" , "Die; decay" , "Suffer complete ruin or destruction" , "Lose one's life" , "Waste away" .)