What does mainlining mean?
Mainlining is an informal term for injecting an illegal drug, especially heroin, directly into a vein. As a noun, it names the practice or act; as a verb, it describes the act of injecting a drug in this way. The expression developed from “main line,” a phrase for a direct route into the bloodstream, making the name grimly literal. In ordinary usage, mainlining is most closely associated with heroin, but writers also use it for other drugs that are injected intravenously, such as cocaine and methamphetamine. Because the subject involves illegal and potentially dangerous drug use, the word often appears in reporting, harm-reduction discussion, or literary portrayals of addiction. It can sound blunt or stigmatizing, so clinical and educational contexts often prefer “injecting drugs” or “intravenous drug use.” Mainlining is useful as a vivid term because it identifies not just drug use in general, but a particular route of administration and its associated risks.
The practice or act of injecting an illicit drug, especially heroin, directly into a vein.
"The documentary examines mainlining and the public-health response."
The singular is often treated as a mass noun; the plural is uncommon.
To inject an illicit drug, especially heroin, directly into a vein.
"The memoir describes a period in which he was mainlining heroin."
Informal and sometimes stigmatizing; “injecting drugs” or “intravenous drug use” is preferred in clinical contexts.
The plural is uncommon because mainlining is normally used as a mass noun.
"The report documented repeated mainlinings of heroin."
A “main line” is a direct route into the bloodstream, making the drug term grimly literal.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does mainlining come from?
Mainlining is formed from main + line, with line continuing Latin linea, originally “linen thread” or “row.” English extended the word to meanings such as a row of writing, a route, and a railway track. In drug vocabulary, the earlier phrase “main line” denoted a direct route into the bloodstream, and mainlining developed from the verb mainline.
Related word forms
How mainlining is actually used
Mainlining is informal and can sound blunt or stigmatizing. Clinical, educational, and harm-reduction contexts often prefer expressions such as “injecting drugs” or “intravenous drug use.”