Not so much heady as potty! (5)
I believe the answer is:
nutty
'potty' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for nutty that I've seen before include "Like cobs, brazils, etc" , "Out to lunch" , "Like brazils, say" , "Crazy -- tasting of almonds" , "passionate" .)