What are Vitamin B12 injections Vitamin B12 injections are used to quickly raise your B12 levels when they're low or when your body can't absorb it properly from food or tablets. What How often should vitamin B12 injections be administered and how frequently should laboratory monitoring be performed? B12 Shots in Friso, Sherman, Anna. and Sunnyvale, TX B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics