Shock plea dropping Ecstasy (5)
I believe the answer is:
appal
'shock' is the definition.
('appal' can be a synonym of 'shock')
'plea dropping ecstasy' is the wordplay.
'plea' becomes 'appeal' (I've seen this before).
'dropping' indicates named letters should be taken away.
'ecstasy' becomes 'e' (informal term for the drug).
'appeal' with 'e' taken away is 'APPAL'.
(Other definitions for appal that I've seen before include "To shock, dismay" , "Dismay, horrify" , "Petrify" , "Outrage" , "Greatly horrify" .)