How to Administer an Intramuscular Injection at Home Instruction Guide for Intramuscular (IM) Self injection of B12 Methylcobalamin 1mg 5mg Dr. prescribed B12 injections. Pharmacy only gave me vials. Where do you get your needles and syringes? What size?? Where do I inject? : r B12_Deficiency Where to Inject Vitamin B12 How to self administer subcutaneous B12 injection., 1. Withdraw proper dosage from vial into an insulin syringe, 2. Clean site of injection (abdomen or other proper site), 3. Pinch the skin where you How to Give a B12 Injection: Step By Step Instructions