B12 Shots Dosage for Adults: How Much, How Often, and Key Injection Guidelines Liv Hospital Vitamin B Complex: Package Insert Prescribing Information Cyanocobalamin is the preferred supplemental form of vitamin B 12 as there is insufficient evidence to support the efficacy of the other forms like methylcobalamin. Michael Greger MD, How Not to Die. 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.