Green’s Dictionary of Slang

1. to inject narcotics directly into a vein.

1938		D. Maurer ‘Lang. of the Und. Narcotic Addict’ Pt 2 in Lang. Und. (1981) 105/2: To main-line. To inject narcotics into the vein.
1952		‘Hal Ellson’ Golden Spike 113: I’d have a whole closet full of H [...] and I’d dive into it and snort and pop and main till I dropped.
1952		T. Southern ‘The Night the Bird Blew for Doctor Warner’ in Southern (1973) 51: I won’t main-line [...] Just skin-popping.
1964		Larner & Tefferteller Addict in the Street (1966) 25: That’s when I started mainlining, when I got to be fifteen. I started mainlining like a dog.
1970		T. Southern Blue Movie (1974) 188: Don’t mainline him, for Chrissake [...] we’ll have a fucking stiff on our hands!
1970		Time 16 Mar. 17: All my friends were on heroin. I snorted a couple of times, skinned a lot, and after that I mained it.
1977		(con. 1960s) Nicholson & Smith Spend, Spend, Spend (1978) 192: He’s the worst fucking junkie [...] He’s mainlined. I’ve been in his place when there’s been blood splattered all over the place from trying to get the junk in his veins.
1985		J. Wambaugh Secrets of Harry Bright (1986) 191: All these crankers’ll tell you they toot it. Bullshit. They mainline it.
1986		C. Bowles G’DAY 25: A muso plays gigs and mainlines.
1993		I. Welsh Trainspotting 31: I reckon that he’s been daein a bit ay mainlining or shit-stabbing on the Q.T.
1996		P. Howard The Joy (2015) [ebook] ‘Skin-popping doesn’t agree with you,’ Duffo said [...] ‘You’d wanna mainline it next time. Put it straight into your vein’.
1999		Africa News Service 29 Nov. 🌐 To get high faster and cheaper he started injecting this straight into his veins, a dangerous method known as ‘mainlining’.
1999		Guardian Guide 22–28 May 7: As Lenny Bruce once said of mainlining smack [it is] ‘like kissing God’.
2000		N. Griffiths Grits 344: A coulduv mainlined inner bogs burrav lost me fuckin spike an am fucked if am gunner use anyone else’s.
2010		K. Richards Life 260: I’ve never mainlined.
2012		C. Stella Rough Riders 54: The fresh needle marks were probably the first two times Nathan Barron had ever mainlined a drug.

2. to inject intravenously in non-drug use; also fig.

1963		in T.I. Rubin Sweet Daddy 30: Here I am mainlining this ammo junk – ammonophiline [i.e. an asthma treatment].
1974		Adamson & Hanford Zimmer’s Essay 104: Watch the speedo. / Plant your foot until the big V8 starts to mainline juice.
1996		K. Lette Mad Cows 67: Half-masting the white flag of surrender she’d been running up to fate, Maddy main-lined that Malteser.
2004		J. Ellroy ‘Hot-Prowl Rape-O’ in Destination: Morgue! (2004) 270: I mainlined some mocha.

3. in fig. use.

1997		T. Fontana ‘Straight Life’ Oz ser. 1 ep. 5 [TV script] Drugs ain’t the only thing to get addicted to. Some people mainline their work. Some people snort ESPN.
2007		L. Redhead Cherry Pie [ebook] [I] drank two cups of coffee (no need to mainline the entire plunger when you weren’t hungover).
2017		T. Spicer Good Girl Stripped Bare 274: I decide to mainline this shit [i.e. the onset of the menopause]. And talk about it all the time.
2024		D. Swierczynski California Bear 1The peanut-buttery scent [of a biscuit] was like mainlining his childhood: .