What is the best route for administering vitamin B12: intramuscular injection or subcutaneous injection? How to self inject intramuscular vitamin B12 Overview Guy's and St Thomas' NHS Foundation Trust B 12 (Methylcobalamin) Therapy MedClub by Dr Jenn How to Give a B12 Injection: Step By Step Instructions 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.