Treatment of initially acute hysteria proven to work (8,7)
I believe the answer is:
aversion therapy
'treatment' is the definition.
(I've seen this before)
'initially acute hysteria proven to work' is the wordplay.
'initially' says to take the initial letters.
'to work' indicates an anagram (letters worked into a new order).
The first letter of 'acute' is 'a'.
'hysteria'+'proven'='hysteriaproven'
'hysteriaproven' is an anagram of 'versiontherapy'.
'a'+'versiontherapy'='AVERSION THERAPY'
'of' is the link.
(Other definitions for aversion therapy that I've seen before include "Behaviour modification technique" , "Type of treatment" , "addict's treatment" , "Medical treatment" .)