Drug injection. Hand of a man injecting a drug (probably heroin) into a vein in his arm. He is using a tourniquet made from string to make the veins stand out. Injection of a drug straight into a vein is known as main lining. It is the preferred route for the most potent opioid analgesics, a group that includes heroin, methadone and morphine. Long term use of these drugs causes tolerance (larger amounts of drug are needed to have the same effect) and dependence (addiction). Infections such as hepatitis B virus and HIV can be spread when addicts share needles. Death commonly occurs from accidental overdose.