Narc
Narc is a shortened form of Narcotic and may refer to hard drugs or, by extension to a police officer from the drugs squad.

NB:
This word is often confused with nark. Nark is British and Australian slang for
(i) noun: a police informer, or more widely, anyone who reports illegal or anti-social activities to any authorities.
(ii) verb: to annoy, to irritate,
"See, that guy over there? The one who looks like a druggie? He's undercover, he's a narc."

"That guy just asked me for money for a cup of coffee"
"Cup of coffee? He's a junky, he wants his narcs."