Make invalid, treated in full, ultimately healthy (7)
I believe the answer is:
nullify
'make invalid' is the definition.
(I've seen this before)
'treated in full ultimately healthy' is the wordplay.
'treated' indicates anagramming the letters.
'ultimately' says to take the final letters.
The last letter of 'healthy' is 'y'.
'in'+'full'='infull'
'infull' with letters rearranged gives 'nullif'.
'nullif'+'y'='NULLIFY'
(Other definitions for nullify that I've seen before include "Declare invalid" , "Bring to naught" , "Make invalid" , "Cancel, abolish" , "Make void" .)