Soothe liver - treatment includes one vitamin, then another (7)
I believe the answer is:
relieve
'soothe' is the definition.
(relieve can mean to soothe)
'liver treatment includes one vitamin then another' is the wordplay.
'treatment' indicates an anagram (letters treated or processed differently).
'includes' is an insertion indicator.
'one vitamin' becomes 'E' (E is an example).
'then another' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'liver' is an anagram of 'reliv'.
'reliv' going around 'e' is 'reliev'.
'reliev'+'e'='RELIEVE'
Can you help me to learn more?
(Other definitions for relieve that I've seen before include "raise a siege" , "Take a job over from - bring aid" , "Allay, alleviate" , "Free someone from duty by taking his place" , "Take over (from) - ease worries (of)" .)