b12 injections where do they inject How to Give Yourself a Injection B12 Shots vs. IV Infusions:

Lipid Metabolism & 3-AR Mechanism Heffernan et al., Endocrinology (2001) Heffernan and colleagues investigated the lipolytic effects of chronic AOD-9604 treatment using two complementary mouse models: diet-induced obese C57BL/6J mice and beta3 adrenergic receptor (3-AR) knockout mice

Vitamin B12 injections are given into a muscle and are commonly used to treat or prevent B12 deficiency in people who need this route

This means the vitamin will get absorbed by the muscle and blood vessels directly

A 1,000 mcg tablet and a 1,000 mcg injection contain the same amount but are absorbed very differently, and oral absorption varies widely from person to person