An intravenous needle
Intravenous (Latin for "within a vein"), IV, or infusion, refers to delivering medicine, fluids, or nutrients into the body's blood via a vein. Veins are commonly used for delivery of fluids and nutrients over time because venous pressure does not vary as much as arterial pressure, permitting more consistent, accurate delivery. Medications that are most effectively delivered over time are commonly administered intravenously, also, either by hypospray or by intravenous unit, or drip.
The puncture site of the needle was sometimes bruised. In 2024, Martin Wells noticed an IV bruise on Jean-Luc Picard's hand, which led him to surmise that the admiral had been treated at the Clinica Las Mariposas. (PIC: "Mercy")
In 2259, Una Chin-Riley suffered an intrusion on her abdominal aorta. Because of the location of a fragment, Chin-Riley was warned that she would bleed a lot and that she would be sedated. Nurse Christine Chapel noted that they had just enough blood plasma but it would need to be given via IV. (SNW: "Memento Mori")
Intravenous injection is impossible for Andorians because of their unusual physiology; instead, a doctor has to opt for intramuscular injection. (TOS: "Whom Gods Destroy")
In 2268, Christine Chapel threatened Ensign Garrovick that Doctor Leonard McCoy would have him intravenously fed if he didn't eat the dinner she had brought him. (TOS: "Obsession")
Intravenous drip
In 2373, Dr. Julian Bashir ordered an IV drip of poly-nutrient solution for Odo after the Changeling's rescue from a Class L planet. (DS9: "The Ascent")