Unending course of treatment for government (6)
I believe the answer is:
regime
'government' is the definition.
(synonyms)
'unending course of treatment' is the wordplay.
'unending' means to remove the last letter (the word doesn't have its end letter).
'course of treatment' becomes 'regimen' (course of medical treatment).
'regimen' with its last letter removed is 'REGIME'.
'for' acts as a link.
(Other definitions for regime that I've seen before include "Government; ordered way of doing something" , "Ruling system" , "Command" , "Dominion of emigre" , "Emigre (anag.)" .)