Green’s Dictionary of Slang

1. (US drugs) a cocaine addict.

1922		Washington Times (DC) 11 June 57/2: He is a ‘leaper’ [...] He fidgets. He fumes. He never sleeps while under the influence of cocaine.
1938		M. Sullivan My Double Life 214: She learned that a cocaine addict is spoken of as a ‘snow-bird’ or a ‘leaper’.
1953		Anslinger & Tompkins Traffic In Narcotics 312: leaper. A cocaine addict.
1973		Maurer & Vogel Narcotics and Narcotic Addiction in Maurer Lang. Und. (1981) 317/1: leapers Users of cocaine who reach an advanced stage where jerky movements resemble St. Vitus dance.

2. (drugs) any form of stimulant, amphetamine etc, usu. in pl.

1961		Rigney & Smith Real Bohemia 63: Known as ‘leapers,’ ‘bennies,’ ‘dexies,’ they are usually swallowed as pills.
1963–74		B. Humphries Barry McKenzie [comic strip] in Complete Barry McKenzie (1988) 39: Look, Bazza, try a couple of leapies and then you’ll really feel like swinging on!
1967		M. Braly On the Yard (2002) 87: The wads of charged cotton [from nasal inhalers] were known as leapers because of the energy and optimism they released in the men who choked them down.
1976		R. Sabbag Snowblind (1978) 240: The most popular word is ups. Brain ticklers, browns, cartwheels, chalk, Christmas trees, coast-to-coasts, dominoes, footballs, greenies, hearts, leapers and truck drivers are words of the sixties and are out of use now.
1987		D. Hebdige Cut ’n’ Mix 110: It’s graceful but the grace is always ‘under pressure’. Fred Astaire on leapers.
2000		Indep. Rev. 19 Feb. 8: Uppers, downers, leapers, acid, coke and flirtations with heroin.

3. a dud cheque, drawn against inadequate funds [note bounce v.² (4)].

1967

J. Breslin World of Jimmy Breslin (1968) 51: He issued a group of checks that were classified as ‘leapers.’.