Green’s Dictionary of Slang

1. to get drunk, thus got on, drunk.

1840		Marryat Poor Jack 366: I’ve been thinking of lowering the quarter boat down, when they are a little more mizzled; they are getting on pretty fast, for Frenchmen haven’t the heads for drinking that Englishmen have.
1842		Bell’s Penny Dispatch 27 Mar. 3/3: Russel got on as usual with brandy-and-water.
1930		G. Milburn ‘Toledo Slim’ in Hobo’s Hornbook 193: And while I sat there drinking, getting on a mighty stew.
1965		B. Jackson Get Your Ass in the Water (1974) 131: I was sittin’ at the table, gettin’ on a mighty stew, / a dead swell dame come sit beside me too.
1972		D. Claerbaut Black Jargon in White America 66: gettin’ on v. 1. reaching inebriation due to excessive drinking.
1999		Eble Campus Sl. Nov. 5: get one’s drink on – satisfy a nervous craving to start drinking excessively.

2. to take drugs, to become intoxicated.

1943		W. Guthrie Bound for Glory (1969) 217: He grabbed the works [...] and bawled both of them out good and proper, telling how terrible it was to get on the stuff.
1952		(con. 1948) G. Mandel Flee the Angry Strangers 33: You wanna get on? I got some pot stashed by the subway.
1963		M. Braly Shake Him Till He Rattles (1964) 61: I can’t get on with this, not even if I shot the whole piece at once.
1969		R.R. Lingeman Drugs from A to Z (1970) 101: get on To take drugs for the first time. [...] getting on Smoking marijuana.
1972		D. Claerbaut Black Jargon in White America 66: gettin’ on v. […] 2. becoming dazed and intoxicated by using drugs.
1980		(con. 1940s–60s) H. Huncke ‘Ed Leary’ in Eve. Sun Turned Crimson (1998) 125: He was anxious by now to get some stuff and get on.

3. to become addicted.

1969

Cressey & Ward Delinquency, Crime, and Social Process 810: He’s lame ... he’s a chump to get off in that bag [...] if he keeps fucking around with it, he’s gonna get on it, gonna get hooked.

4. (Aus. prison) to buy drugs.

1990

Tupper & Wortley Aus. Prison Sl. Gloss. 🌐 Get on. To obtain drugs; to score.