B12 Injection Dose: 7 Key Guidelines for Adults and Common Prescriptions Liv Hospital B12 Injections vs. Oral Supplements: Which Is Better? 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 Seven reasons you may need a B12 boost Vitamin B12 injections deliver high doses of this essential vitamin directly into your bloodstream for better absorption than oral supplements to boost energy, support red blood cell production and maintain nerve function.