B12 Injection Frequency: How Often Should You Get a B12 Shot? Liv Hospital Gym goers spending monthly on vitamin B and C injections Have a f*cking word with yourself. Both are water soluble, so don't stick around for long in your system (12 14hrs) hence Vitamin B12 Injections Specialist in Langhorne, PA B12 Injection sites + How to use B12 Shots Safely How often should vitamin B12 injections be administered and how frequently should laboratory monitoring be performed?