Intended receiver may see a daughter shift ecstasy repeatedly (9)
I believe the answer is:
addressee
'intended receiver' is the definition.
(person a letter or package is addressed to)
'a daughter shift ecstasy repeatedly' is the wordplay.
'daughter' becomes 'd' (genealogical abbreviation).
'shift' becomes 'dress' (shift can mean a dress).
'ecstasy' becomes 'E' (informal term for the drug).
'repeatedly' indicates the doubling of some letters.
'e' duplicated is 'ee'.
'a'+'d'+'dress'+'ee'='ADDRESSEE'
'may see' acts as a link.
(Other definitions for addressee that I've seen before include "He's written to" , "one who's likely to get the post" , "The person to whom letter is delivered" , "Person whose name is on the envelope" , "The one to whom the message is sent" .)