It's taken as a medicine; not a diet properly (8)
I believe the answer is:
antidote
'it's taken' is the definition.
I can't judge whether this definition defines the answer.
'a medicine not a diet properly' is the wordplay.
'not a diet' anagrams to 'ANTIDOTE'.
But, I'm not clear how this is indicated.
'as' acts as a link.
Can you help me to learn more?
(Other definitions for antidote that I've seen before include "It counteracts poison" , "Counter-measure" , "Medicine countering a poison" , "Tied to an awful counteracting agent" , "It makes you feel better" .)