One who injects drugs into their bloodstream with a needle.
Ohmygod, he's not only a mainliner, he reuses his works! Do not exchange any bodily fluids with him no matter what.
by mjrn February 25, 2006
1 more definition
One who does drugs such as heroin by means of shooting up in a vein. Intraveinously
Hes a mainliner druggie
by Kyleigh January 26, 2006