Different Types Of Needles: Know About The Gauge, Length & Sizes A vitamin B12 injection is a shot that delivers B12 directly into your muscle, helping your body absorb it quickly (especially if your body struggles to absorb it from food or tablets) Vitamin b12 Injection CardioMender, MD How to self inject intramuscular vitamin B12 Overview Guy's and St Thomas' NHS Foundation Trust Not all shots are the same here's a guide Injections are a fast, effective way to deliver medications, nutrients, and vaccines directly into the body but not all injections are the same.