Intramuscular Injection

Intramuscular (IM) injection deposits the dose into the body of a skeletal muscle, where dense vascularization produces faster systemic uptake than the SC route. IM is the standard route for vaccines and is sometimes preferred for peptides whose target tissue is muscle (MGF, TB-500 for muscle injuries).

Common IM sites include the deltoid, vastus lateralis, gluteus medius, and ventrogluteal region. IM injection requires a longer needle than SC — typically 22–25G, 1 to 1.5 inches — to reach the muscle belly through the fat layer.

Pinch-and-poke is acceptable for SC but contraindicated for IM; aspiration is no longer recommended in current clinical guidance for most IM sites.