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 Vitamin B12 Injection Dose For Adults Consensus Academic Search Engine Choosing the Right Needle and Syringe for B12 Injections: A Complete Guide Question of the Day:, How long does it take for a B12 injection to rev up the engines of energy? , For many people, the boost can be felt within 2448 hours. Others may notice gradual changes