As in medicines raved over (7)
I believe the answer is:
arsenic
'as' is the definition.
('arsenic' can be a synonym of 'as')
'in medicines raved over' is the wordplay.
'in' indicates the answer is hidden within the clue.
'over' is a reversal indicator.
'cinesra' is hidden within 'medicines raved'.
'cinesra' reversed gives 'ARSENIC'.
(Other definitions for arsenic that I've seen before include "killer" , "Brittle grey-green semi-metal, atomic number 33" , "Ratsbane" , "As briefly identified" , "Element with many poisonous compounds" .)