Excessive measure restricting Ecstasy (5)
I believe the answer is:
steep
'excessive' is the definition.
(thesaurus)
'measure restricting ecstasy' is the wordplay.
'measure' becomes 'step' (step is a kind of measure**).
'restricting' indicates putting letters inside.
'ecstasy' becomes 'e' (informal term for the drug).
'step' going around 'e' is 'STEEP'.
(Other definitions for steep that I've seen before include "Quickly rising" , "Having a sharp incline" , "Stiff - thoroughly wet" , "Unreasonably dear - soak" , "Almost perpendicular" .)