Adult partner takes Ecstasy with just a little apple juice (4,4)
I believe the answer is:
aloe vera
'juice' is the definition.
(I've seen this before)
'adult partner takes ecstasy with just a little apple' is the wordplay.
'adult' becomes 'a'.
'partner' becomes 'e'.
'takes' is an insertion indicator (take can mean to capture or invade).
'ecstasy with' becomes 'lover' (I can't explain this - if you can you should give a lot more credence to this answer).
'just a little' says to take the initial letters.
The initial letter of 'apple' is 'a'.
'e' placed inside 'lover' is 'loever'.
'a'+'loever'+'a'='ALOE VERA'
(Other definitions for aloe vera that I've seen before include "Plant substance used in cosmetics" , "Succulent" , "Cosmetic plant extract" , "cosmetic juice" , "Plant with juice used for treating burns" .)