Ecstasy dropped into the wine as principle? (5)
I believe the answer is:
tenet
'principle?' is the definition.
(a tenet is a principle or value)
'ecstasy dropped into the wine' is the wordplay.
'ecstasy' becomes 'E' (informal term for the drug).
'dropped into' indicates putting letters inside.
'the wine' becomes 'tent' (type of Spanish wine).
'e' inserted into 'tent' is 'TENET'.
'as' acts as a link.
(Other definitions for tenet that I've seen before include "Matter of belief" , "A belief or credo - it's a palindrome" , "That's the law" , "Adiaphoron" , "you may believe in it" .)