Does size matter? Historically, a bigger needle gauge was considered better to prevent damage to red blood cells. However, our recent guidelines recommend using smaller gauge needles (2325 G) for all Choosing the Right Needle and Syringe for B12 Injections: A Complete Guide 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 Needle Sizes Explained: Choosing the Right Gauge for Different Injections B12 vitamin Store Intramuscular vs Subcutaneous Injections for vitamin B12 supplements. Ivy Grove Surgery : Self administration of B12 injection