Influenced in an unnatural way (8)
I believe the answer is:
affected
I believe this clue is a double definition.
'influenced' is the first definition.
(I've seen this before)
'in an unnatural way' is the second definition.
(Other definitions for affected that I've seen before include "attacked" , "Impacted on" , "Influenced; pretentious" , "Artificial in manner, phoney" , "La-di-da" .)