A hypodermic needle is a hollow needle commonly used with a syringe to inject substances into the body or extract fluids from it. They may also be used to take liquid samples from the body, for example taking blood from a vein in venipuncture. Large-bore hypodermic intervention is especially useful in treating catastrophic blood loss or shock.

A hypodermic needle also provides for rapid delivery of liquids. It is also used when the injected substance cannot be ingested orally, either because it would not be absorbed, as with insulin, or because it would harm the liver.