main·line 
(mānlīn′)
(mānlīn′)v. main·lined, main·lin·ing, main·lines
Informal
Informal
v.tr.
To inject (an illegal or addictive drug, such as heroin) directly into a major vein.
v.intr.
To inject a drug intravenously.
adj.
Being in a principal or well-established position: the mainline churches.
mainlin′er n.