B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Instruction Guide for Intramuscular (IM) Self injection of B12 Methylcobalamin 1mg 5mg Common IM Injection Sites Deltoid (Upper Arm) Location: About 23 finger widths below the acromion process (shoulder bone). Best for: Vaccines and small volume injections (1 mL). Notes: Easy to access but limited Nurse Administering B12 Shot Arm Will a Vitamin B12 Injection Give Me More Energy? Subcutaneous Injection: What It Is and How to Give One