Soporific drug helps eating disorder (8,7)
I believe the answer is:
sleeping draught
'soporific' is the definition.
(sleeping draught is a kind of soporific)
'drug helps eating disorder' is the wordplay.
'disorder' indicates anagramming the letters (I've seen 'diseased' mean this (I've seen this in other clues)).
'drug'+'helps'+'eating'='drughelpseating'
'drughelpseating' is an anagram of 'SLEEPING-DRAUGHT'.
(Other definitions for sleeping draught that I've seen before include "This should make for a quiet night" , "Soporific" .)