<unk> , often abbreviated<unk> , is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications.<unk>  may be preferred because muscles have larger and more numerous blood vessels than subcutaneous tissue, leading to faster absorption than subcutaneous or intradermal injections. Medication administered via<unk>  is not subject to the first-pass metabolism effect which affects oral medications. Common sites for<unk> s include the deltoid muscle of the upper arm and the gluteal muscle of the buttock. In infants, the vastus lateralis muscle of the thigh is commonly used. The injection site must be cleaned before administering the injection, and the injection is then administered in a fast, darting motion to decrease the discomfort to the individual. The volume to be injected in the muscle is usually limited to 2–5 milliliters, depending on injection site. A site with signs of infection or muscle atrophy should not be chosen.<unk> s should not be used in people with myopathies or those with trouble clotting.<unk> s commonly result in pain, redness, and swelling or inflammation around the injection site. These side effects are generally mild and last no more than a few days at most. Rarely, nerves or blood vessels around the injection site can be damaged, resulting in severe pain or paralysis. If proper technique is not followed,<unk> s can result in localized infections such as abscesses and gangrene. While historically aspiration, or pulling back on the syringe before injection, was recommended to prevent inadvertent administration into a vein, it is no longer recommended for most injection sites by some countries.
Intramuscular injection
Subcutaneous injection
Intraperitoneal injection
Subcutaneous infusion
Subcutaneous implant
Intrathecal administration
Intradermal injection
Transdermal spray