Irregular therapy disheartened sufferer (8)
I believe the answer is:
casualty
'sufferer' is the definition.
(a person killed)
'irregular therapy disheartened' is the wordplay.
'irregular' becomes 'casual' (similar in meaning).
'disheartened' suggests removing the centre.
'therapy' with its middle taken out is 'ty'.
'casual'+'ty'='CASUALTY'
(Other definitions for casualty that I've seen before include "A cult, say (anag.)" , "Hospital department" , "a person getting injured" , "Wounded victim" , "One killed or hurt in accident or war" .)