Harass healers to despair (4,5)
I believe the answer is:
lose heart
'despair' is the definition.
(both can mean to feel hopeless)
'harass healers to' is the wordplay.
'harass' indicates an anagram (I've seen 'harassing' mean this).
'healers'+'to'='healersto'
'healersto' is an anagram of 'LOSE HEART'.
(Other definitions for lose heart that I've seen before include "Falter in courage - or fall in love? (4, 5)" , "Mislay a card" , "Become disillusioned" , "Here's a lot to cause courage to ebb" , "What patient may do before subsequent transplant" .)