Mainlining is a term that is commonly used to refer to the intravenous injection of drugs. However, there are many synonyms for this word that can be used to describe this action in different ways. Some of the most common synonyms for mainlining are shooting up, getting a fix, injecting, and dosing up. Other synonyms include shooting, slamming, poking, and jabbing. These words all refer to the same basic action of injecting drugs directly into the bloodstream, but they vary in their connotations and levels of formality. Regardless of which synonym is used, all of these words describe a potentially dangerous and harmful behavior that can lead to serious health complications.