diagram of the vitamin b12 injection site are injections subcutaneous or intramuscular How to Give B12 Injections at Home to Yourself · PA Vitamin B12 Injections Clinic Near
Description
Cleveland Clinic

They are injected directly into the bloodstream, making them more effective than oral supplements
Balancing a checkbook becomes an exercise in higher math
Hepatology 56 , 21542162 (2012)
This is why supplementation starts day 1 post-op not when you feel you need it

Together with B-vitamin fortified food (e.g., cereal, nutritional yeast) and supplements, these foods might contribute, though modestly, to prevent vitamin B 12 deficiency in individuals consuming vegetarian diets