Taking drugs resulting in accountant leaving (5)
I believe the answer is:
using
'taking drugs' is the definition.
(using drugs)
'resulting in accountant leaving' is the wordplay.
'resulting in' becomes 'causing' (I've seen this in another clue).
'accountant' becomes 'ac'.
'leaving' is a deletion indicator.
'causing' with 'ac' taken away is 'USING'.
(Other definitions for using that I've seen before include "Putting into service" , "Utilising" , "practice" , "Putting to a particular purpose" , "taking drugs" .)