Tricked theologian to keep up on ecstasy (5)
I believe the answer is:
duped
'tricked' is the definition.
(I've seen this before)
'theologian to keep up on ecstasy' is the wordplay.
'theologian' becomes 'dd' (Doctor of Divinity degree).
'to keep' is an insertion indicator.
'up on' becomes 'up' ('up' can be similar in meaning to 'up on').
'ecstasy' becomes 'e' (informal term for the drug).
'up'+'e'='upe'
'dd' going around 'upe' is 'DUPED'.
(Other definitions for duped that I've seen before include "Hoodwinked and misled" , "Bamboozled" , "Fooled, codded" , "Deceived" , "Taken for a ride" .)