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. Vitamin B12 Injections vs. Supplements: Which is Right for You? B12 Injections vs Supplements: 16 Key Facts Explained 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 B12 Injections vs. Oral Supplements: Which Works Better?