Tortured artist swallows Ecstasy before English essay (8)
I believe the answer is:
treatise
'essay' is the definition.
(I've seen this before)
'tortured artist swallows ecstasy before english' is the wordplay.
'tortured' is an anagram indicator (I've seen this in other clues).
'swallows' is an insertion indicator.
'ecstasy' becomes 'e' (informal term for the drug).
'before' says to put letters next to each other.
'english' becomes 'e' (abbreviation).
'artist' anagrammed gives 'tratis'.
'tratis' going around 'e' is 'treatis'.
'treatis'+'e'='TREATISE'
(Other definitions for treatise that I've seen before include "Disquisition" , "Essay on theme" , "Learned paper" , "Academic composition" , "Long, detailed essay" .)