A poet is destroyed by drugs (7)
I believe the answer is:
opiates
'drugs' is the definition.
(opiate is a kind of drug)
'a poet is destroyed' is the wordplay.
'destroyed' indicates anagramming the letters.
'a'+'poet'+'is'='apoetis'
'apoetis' anagrammed gives 'OPIATES'.
'by' is the link.
(Other definitions for opiates that I've seen before include "Poppy-derived drugs" , "Sedative drugs" , "Narcotic drugs" , "Makes dull" , "Is a poet (anag.)" .)