Vitamin B12 is a water-soluble vitamin that plays an important role in brain function and red blood cell production.
Those at greatest risk of vitamin B12 deficiency are vegans and vegetarians, who get little to no B12 from their diet. Deficiency can also be caused by poor absorption.
If you are deficient in vitamin B12, then the injections are very effective at raising your blood levels.
Vitamin B12 injections are very safe. In rare cases, the injections may cause allergic reactions.