Superior twice taking tablets, intoxicated by drug (2,4,4,5)
I believe the answer is:
on ones high horse
'superior' is the definition.
'twice taking tablets intoxicated by drug' is the wordplay.
'twice taking' becomes 'onon' (I can't explain this - if you can you should believe this answer much more).
'tablets' becomes 'es' (E can refer to an ecstasy tablet).
'intoxicated' becomes 'high' ('high' can be similar in meaning to 'intoxicated').
'by' says to put letters next to each other.
'drug' becomes 'horse' (horse is a slang term for heroin).
'onon'+'es'+'high'+'horse'='ON ONES HIGH HORSE'
(Other definitions for on ones high horse that I've seen before include "in an attitude of smug superiority" , "Overbearing" , "With an air of superiority" , "like George IV in Trafalgar Square?" .)