Herbal drink served up — it's all there (6)
I believe the answer is:
tisane
'herbal drink' is the definition.
(I've seen this in another clue)
'up it's all there' is the wordplay.
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'all there' becomes 'sane' ('not all there' can mean insane).
'it' back-to-front is 'ti'.
'ti'+'sane'='TISANE'
'served' acts as a link.
(Other definitions for tisane that I've seen before include "Infusion of e.g. dried or fresh flowers or leaves" , "Herb tea" , "Herbal tea drink" , "Infusion (eg of herbs or flowers)" , "Herbal infusion" .)