Effective power of the disheartened and the deranged (5)
I believe the answer is:
teeth
'effective power' is the definition.
(I've seen this before)
'the disheartened and the deranged' is the wordplay.
'disheartened' suggests removing the centre (the middle or heart is removed).
'and' is a charade indicator (letters next to each other).
'deranged' is an anagram indicator.
'the' with its centre removed is 'te'.
'the' anagrammed gives 'eth'.
'te'+'eth'='TEETH'
'of' is the link.
(Other definitions for teeth that I've seen before include "Those of wisdom" , "genuine power" , "Projections on a gear" , "Molars, incisors, etc" , "rarely a hen's" .)