Green’s Dictionary of Slang

1. (orig. US) to work (something) out, to assess, esp. in working out possible winners in a horserace.

1901		‘Hugh McHugh’ Down the Line 14: I confided to her the fact that I doped a turtle named ‘Pink Toes’ to win the next day.
1902		C.L. Cullen More Ex-Tank Tales 6: I doped it that when he wanted to tip me off as to his lay he’d do it.
1906		‘O. Henry’ ‘The Green Door’ in Four Million (1915) 163: I believe it was the hand of Fate that doped out the way for me to find her.
c.1910		H.E. Lee ‘Tough Luck’ Variety Stage Eng. Plays 🌐 Pretty Girl —I wonder has it a chance to win? I doped it all out last night and it seems to me that it can’t lose.
1915		G. Bronson-Howard God’s Man 215: Set your think-box going and dope out a way for three smart young fellows to grab a chunk of perfectly good green stuff.
1921		N. Putnam West Broadway 53: By about nine-thirty we had a route to Los Angeles all doped out.
1923		D. Hammett ‘House Dick’ in Nightmare Town (2001) 54: That’s how I doped it [...] and I reckon it’s about right.
1925		Dos Passos Manhattan Transfer 355: I been dopin out a lot of things these last few days.
1931		C.B. Yorke ‘Snowbound’ in Gangster Stories Oct. n.p.: I thought I had things doped out.
1935		(con. 1920s) J.T. Farrell Judgement Day in Studs Lonigan (1936) 541: That’s the way I always doped him.
1937		D. Fuchs Low Company 125: In the sixth race he had already doped out a beauty.
1940		D. Maurer Big Con 66: Nobody had doped it [i.e. a horserace] out that way.
1940		R.L. Bellem ‘Death’s Passport’ in Goodstone Pulps (1970) 114/2: We’ve got to dope up a scheme to bring him back to the public.
1944		D. Runyon Runyon à la Carte 72: It all works out just like I dope it.
1950		P. Highsmith Strangers on a Train (1974) 30: Want me to dope out a perfect murder of your wife for you?
1952		Lait & Mortimer USA Confidential 173: Meanwhile efficiency languishes while skilled workmen waste much time doping form and getting results after each race.
1959		W. Brown Teen-Age Mafia 133: The cops doped it out that he was an idiot.
1962		K. Amis letter 27 July in Leader (2000) 605: I’m sure that between us we can dope out something which will, if not give the readers of SHOW what they want, at any rate do them good.
1978		T. O’Brien Going After Cacciato (1980) 13: He had it all doped out.
1999		Guardian 20 Aug. 26: The way I have it doped, all we have to fear is the growing might of Russia.
2022		J. Hannaham Didn’t Nobody Give a Shit 57: She doped out how oblivious or unmoved her family had been during all the earthquakes of her life story.

2. to feed biased or inaccurate information to someone.

3. (Aus. / US) to explain, to inform, to recount; US use constr. with in, .

1904		Sydney Sportsman (Surry Hills, NSW) 5 Oct. 3/7: Let me dope you, gentle reader, the proper, up-to-date version of the Golden Rule.
1963		T.I. Rubin Sweet Daddy 72: Doc Smith has doped me into plenty.
1968		H. Sackler Great White Hope II iii: Well, the boys’ll dope me in.