Hormone found within on both sides of skull, oddly (7)
I believe the answer is:
insulin
'hormone' is the definition.
(insulin is a kind of hormone)
'within on both sides of skull oddly' is the wordplay.
I cannot quite see how this works, but
'within' could be 'in' and 'in' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'found' acts as a link.
Can you help me to learn more?
(Other definitions for insulin that I've seen before include "Hormone regulating the amount of glucose in the blood" , "Secretion, deficiency of which results in diabetes" , "body needs it" , "Hormone controlling sugar supply" , "blood sugar regulated by this" .)