Alternatively, gone crazy about a herb (7)
I believe the answer is:
oregano
'herb' is the definition.
(I know that oregano is a type of herb)
'alternatively gone crazy about a' is the wordplay.
'alternatively' becomes 'or'.
'crazy' indicates anagramming the letters.
'about' is an insertion indicator.
'gone' anagrammed gives 'egno'.
'egno' enclosing 'a' is 'egano'.
'or'+'egano'='OREGANO'
(Other definitions for oregano that I've seen before include "that's aromatic" , "Dried marjoram" , "Kitchen herb" , "Marjoram-like herb" , "food flavouring" .)