Green’s Dictionary of Slang

(drugs) cocaine.

1922		E. Murphy Black Candle 184: The finest grade of cocaine in the world is manufactured in Germany and is known as ‘Mercks’.
1976		K. R. Sabbag Snowblind (1978) 72: ‘Merck’, as it is commonly called, is cocaine hydrochloride.
2001		ONDCP Street Terms 15: Merck [...] Merk — Cocaine.
2013		T. Dorsey Riptide Ultra-Glide 22: Coke [...] Charlie, Chippy, Belushi, Foo-Foo, Merck, mojo, movie star [etc].