Green’s Dictionary of Slang

(UK Und.) a knockout drug made from laudanam; used by brothel keepers to initiate young girls into the trade.

1885

W.H. Stead ‘How Girls Are Bought and Ruined’ in Pall Mall Gazette in Metropolitan Poor III 14: I gave her a drowse. It is a mixture of laudanam and something else. Sometimes chloroform is used, but I always use snuff or laudanam. We call it drowse of black draught [...] the girl never knows what has happened.