Optimal B12 Injection Sites for Maximum Absorption and Benefits Your Health Magazine At Home Vitamin B12 4 Week Injection Package MUST BE A FLORIDA RESID CardioMender, MD How to Administer an Intramuscular Injection at Home 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 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