Intramuscular Injection

Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle, one of several methods of parenteral medication administration. It may be preferred because muscles have larger and more numerous blood vessels than subcutaneous tissue, giving faster absorption than subcutaneous or intradermal injection, and medication given this way avoids the first pass metabolism effect that affects oral medications. Common sites include the deltoid muscle of the upper arm and the gluteal muscle of the buttock, with the vastus lateralis of the thigh commonly used in infants; side effects are usually mild pain, redness, and swelling, though rare complications include nerve or blood vessel damage or, without proper technique, localized infections such as abscesses and gangrene.