Current means of identifying hallucinogen (4)
I believe the answer is:
acid
'hallucinogen' is the definition.
(acid is a kind of hallucinogen)
'current means of identifying' is the wordplay.
'current' becomes 'ac' (alternating current).
'means of identifying' becomes 'ID' (identification).
'ac'+'id'='ACID'
(Other definitions for acid that I've seen before include "Corrosive liquid; drug" , "So-called drug" , "something sharp" , "Drug LSD (colloq.)" , "Sour to the taste" .)