Situation with inadequate leader: such will be ineffective (8)
I believe the answer is:
placebos
'such will be ineffective' is the definition.
(placebos have no effect)
'situation with inadequate leader' is the wordplay.
'situation' becomes 'place' (synonyms).
'with' is a charade indicator (letters next to each other).
'inadequate' means to remove the last letter (an incomplete or inadequate form of the word).
'leader' becomes 'boss' (boss is a kind of leader).
'boss' with its last letter taken away is 'bos'.
'place'+'bos'='PLACEBOS'
(Other definitions for placebos that I've seen before include "Inert medications, given in drug trials" , "Physically inactive medicines" , "Inactive drugs" , "Medications with no medicinal content" , "Useless drugs" .)