B12 vitamin Store Intramuscular vs Subcutaneous Injections for vitamin B12 supplements. 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 like, swipe, and save for when it's your turn to do an injection on a patient Intramuscular (IM) Angle: 90 Needle Size: 2225G, 11.5 inch Med Examples: Vaccines (e.g. Tdap,