I notice a burst of energy for a couple of days after my injection. My ferritin level was 11 and it did go up to 16 (I can't take iron), but I was doing weekly injections. If your B12 is low you do need to supplement. If it's not too low sublingual might do it for you. Don't ignore low B12 it can lead to all kinds of neurological problems. I was diagnosed with nerve damage before anyone checked my B12 level. Maybe not the total cause but low B12 can cause it.