A Z-track injection of medication is an intramuscular injection that eliminates tracking residual medication through sensitive tissues. A needle and syringe are used to inject medication into a large muscle. The large muscle traps the medication by sealing it deep within the structure of the muscle fiber. The muscle-seal permits no exit of the medication back into subcutaneous tissue or skin. Z-track injections are often used for medications that can be highly irritating to sensitive tissue, like the medication vistaril, and for injecting dark colored medications that can stain sensitive tissue, like iron solutions.