Intramuscular (IM) is used to deliver a medication deep into the muscles. This allows the medication to be absorbed into the bloodstream quickly. IM injections are absorbed faster than Sub-Q injections because muscle tissue has a greater blood supply than the tissue just under the skin. Muscle tissue can also hold a larger volume of medication than subcutaneous tissue.

Subcutaneous (Sub-Q) is used to deliver a medication into the fat layer between the skin and the muscle. Subcutaneous injections are used to give small amounts and certain kinds of medicine.

Intravenous (IV) is commonly used to administer fluids, medications and nutrients directly into a person’s vein. It’s the fastest way to deliver medications and fluid replacement throughout the body as they are introduced directly into the circulatory system and thus quickly distributed.

Intradermal (ID) s a shallow or superficial injection of a substance into the dermis to obtain a faster systemic uptake compared with subcutaneous injections.