That depends on your body and why you are deficient. People who cannot absorb B-12 will need regular injections since your body needs B-12 to function properly. If you can absorb B-12 and have simply developed a deficiency you will only need enough to build up your reserves.
When injections are first administered a patient with severe symptoms may receive 4 to 7 during the first week to restore the body’s reserves of this vitamin. The effects are powerful and quick, most patients see and feel a positive response within 48 to 72 hours with a brisk production of new red blood cells. Along with that comes a boost of energy and fatigue diminishes.