Attempt to speak in support of drugs (5)
I believe the answer is:
essay
'attempt' is the definition.
(essay is a kind of attempt)
'speak in support of drugs' is the wordplay.
'speak' becomes 'say' (I've seen this before).
'in support of' is a charade indicator (letters next to each other) (I've seen this in other clues).
'drugs' becomes 'es' (ecstasy tablets).
'say' after 'es' is 'ESSAY'.
'to' is the link.
(Other definitions for essay that I've seen before include "Thesis" , "Attempt - piece of writing" , "Written composition" , "Composition, paper, article" , "Trial, piece of writing" .)