Vitamin B12 shots: Uses, benefits, and side effects What Is a Vitamin B12 Injection, and How Does It Work? Advice, Tips and News Vitamin B12 Dosage for Seniors: What It Does and How Much to Take Snug Safety How to Give a B12 Injection: Step By Step Instructions How To Give B12 Injection + Benefits 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