Pain-killer remodelled hair-mop (7)
I believe the answer is:
morphia
'pain-killer' is the definition.
(I know that morphia is a type of painkiller)
'remodelled hair-mop' is the wordplay.
'remodelled' indicates anagramming the letters.
'hair'+'mop'='hairmop'
'hairmop' anagrammed gives 'MORPHIA'.
(Other definitions for morphia that I've seen before include "Opiate" , "hypnotic drug" , "Painkilling drug" , "Sedative" .)