What is the method of delivering substances directly into the bloodstream through a vein?

The method of delivering substances directly into the bloodstream through a vein is termed intravenous administration. In this process, a substance—such as medication or fluids—is injected directly into a person's venous system, allowing for immediate absorption and effect. This method is particularly useful for quick therapeutic responses, providing a precise control over dosage and the ability to deliver large volumes efficiently.

In contrast, intradermal injection involves administering substances into the dermal layer of the skin, which is not suitable for immediate systemic absorption. Subcutaneous injections deliver substances into the layer of fat beneath the skin, and while they can be absorbed into the bloodstream, the onset of action is slower compared to intravenous methods. Intramuscular injections introduce substances into a muscle, which may also absorb medication effectively but does so less rapidly than intravenous delivery.