Drink made from bananas, full of energy (4)
I believe the answer is:
mead
'drink' is the definition.
(mead is a kind of drink)
'bananas full of energy' is the wordplay.
'bananas' becomes 'mad' (slang for insane).
'full of' indicates putting letters inside.
'energy' becomes 'e' (physics symbol as in E=mc2).
'mad' placed around 'e' is 'MEAD'.
'made from' is the link.
(Other definitions for mead that I've seen before include "The poetic field" , "sweet drink" , "Cooked joint" , "Alcoholic drink of fermented honey and water of old" , "Alcoholic drink made with honey" .)