How Often Should You Get B12 Injections? When that Vitamin B12 injection kicks in , B12 helps boost your energy, improve mood, support brain function & metabolism, and even strengthen hair, skin + nails , Who doesnt love a healthy 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 B12 Injection Frequency: How Often Should You Get a B12 Shot? Liv Hospital