Permanently give up excess consumption ... (3,4)
I believe the answer is:
for good
'permanently' is the definition.
(I've seen this before)
'give up excess consumption' is the wordplay.
'give up' becomes 'forgo' ('forgo' can be a synonym of 'give up').
'excess consumption' becomes 'od' (abbreviation for overdose).
'forgo'+'od'='FOR GOOD'
(Other definitions for for good that I've seen before include "Permanently - that's not bad" , "Purpose of charitable work" , "Permanently, always" , "Informally, once and for all" , "on the side of the angels" .)