Intelligence is causing considerable pain (6)
I believe the answer is:
smarts
'intelligence' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for smarts that I've seen before include "is painful" , "Stings or rankles" , "Hurts; stings" , "Stings painfully" , "Aged dandies" .)