When someone mainlines heroin, how are they taking the drug?

Mainlining heroin refers to the method of administration where the drug is injected directly into the bloodstream. This process allows for rapid onset of effects as the heroin bypasses the digestive system and enters the circulatory system immediately. The term "mainline" specifically indicates this intravenous injection as it provides the user with intense and immediate effects compared to other methods of use.

In contrast, smoking heroin would involve inhaling the fumes created by heating the substance, while snorting would mean taking the drug through the nasal passages. Both of these methods result in slower absorption and onset of effects compared to injecting, making them distinctly different from mainlining.