How to Give a B12 Injection: Step By Step Instructions B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Deltoid Intramuscular Injection: Technique, Site, and Risks B12 vitamin Store Intramuscular vs Subcutaneous Injections for vitamin B12 supplements. Vitamin B12 Injections 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