The drug, a disaster, but it's relative (8)
I believe the answer is:
daughter
'it's relative' is the definition.
(daughter is a kind of relative)
'the drug a disaster' is the wordplay.
'disaster' indicates an anagram.
'the'+'drug'+'a'='thedruga'
'thedruga' anagrammed gives 'DAUGHTER'.
'but' is the link.
(Other definitions for daughter that I've seen before include "'''Don't put your ... on the stage, Mrs Worthington'' (Noel Coward) (8)'" , "Close relative" , "Relation" , "Female descendant" , "Female child" .)