An intravenous injection is defined as giving medication directly into a vein. It allows for rapid absorption and is used when oral administration is not possible. The main types are peripheral and central lines. IV injection ensures the full dosage is received and can administer medications that cannot be taken orally. Proper procedure and aseptic technique are required to prevent infection. Potential risks include pain, infection, fluid overload and embolism. It provides complete bioavailability but requires technical ability and carries more risk than other routes of administration.