Choice of alternative potion (6)
I believe the answer is:
option
'choice' is the definition.
('option' can be a synonym of 'choice')
'alternative potion' is the wordplay.
'alternative' is an anagram indicator.
'potion' anagrammed gives 'OPTION'.
'of' is the link.
(Other definitions for option that I've seen before include "The choice of taking or leaving" , "Choice, selection" , "Alternative for choice" , "Altenative choice" , "Right to choose" .)