Remedy, counteragent (8)
I believe the answer is:
antidote
I believe this clue is a double definition.
'remedy' is the first definition.
(I know that antidote is a type of remedy)
'counteragent' is the second definition.
(thesaurus)
(Other definitions for antidote that I've seen before include "It makes you feel better" , "Donate it to anti-poison agent" , "Tied to an awful counteracting agent" , "Counterpoison" , "Counteractive medicine" .)