This document discusses intravenous injection (IV), which delivers liquid substances directly into a vein. IV injection allows for fast action of medications and fluid replacement throughout the body. It defines IV injection as introducing a small quantity of drug into a vein via venous puncture. The purposes of IV injection are to have a fast drug action during emergencies, administer irritating or ineffective oral medications, and have drug actions on the bloodstream. Potential complications include infiltration, hematoma, air embolism, and allergic reactions.