Note European drug detective's obligations (5)
I believe the answer is:
needs
'obligations' is the definition.
(I've seen this in another clue)
'note european drug detective's' is the wordplay.
'note' becomes 'n' (abbreviation).
'european' becomes 'E' (abbreviation e.g. EU).
'drug' becomes 'e' (E is another name for ecstasy).
'detective' becomes 'DS' (detective sergeant).
'n'+'e'+'e'+'ds'='NEEDS'
(Other definitions for needs that I've seen before include "Misses" , "Necessities" , "Is desperate for" , "Requires, is in want of" , "Requires or lacks" .)