Last character on ecstasy had a lot initially, with enthusiastic devotion (4)
I believe the answer is:
zeal
'enthusiastic devotion' is the definition.
(I've seen this in another clue)
'last character on ecstasy had a lot initially' is the wordplay.
'last character' becomes 'Z'.
'on' says to put letters next to each other.
'ecstasy' becomes 'E' (informal term for the drug).
'had' says to put letters next to each other.
'initially' indicates taking the first letters.
The first letter of 'lot' is 'l'.
'z'+'e'+'a'+'l'='ZEAL'
'with' acts as a link.
(Other definitions for zeal that I've seen before include "Intense enthusiasm" , "(Excessive) fervour" , "Interest that's definitely not diminished" , "Militancy" , "6 [ENTHUSIASM]" .)