How Often Can I Take B12 Injections? B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics How long after initiating vitamin B12 (cobalamin) injections should lab work be rechecked for a patient with an initial vitamin B12 level of 173, which is below the normal range? Vitamin B12 is essential for energy production, nervous system function, and red blood cell formation. However, oral B12 supplementation doesn't work well for everyoneabsorption can be limited by digestive issues, certain medications, How Quickly Do Vitamin B12 Injections Work? Prime Aesthetics