Remedy: criticise one with added vitamin (7)
I believe the answer is:
panacea
'remedy' is the definition.
(I know that panacea is a type of remedy)
'criticise one with added vitamin' is the wordplay.
'criticise' becomes 'pan' (informal term meaning to criticise heavily).
'one' becomes 'ace' (ace has a value of one in some card games).
'with added' says to put letters next to each other.
'vitamin' becomes 'A' (A is an example).
'pan'+'ace'+'a'='PANACEA'
(Other definitions for panacea that I've seen before include "that's going to help a lot" , "offering solution to all ills" , "fixes all complaints" , "A cure-all for diseases or troubles" , "Nostrum" .)