The main reason that a doctor would prescribe vitamin B12 injections is if the patient is unable to obtain enough vitamin B12 on their own, whether they have pernicious anemia or are unable to get enough of the vitamin through their diet alone
Maar, K., Hetenyi, R., Maar, S., Faskerti, G., Hanna, D., Lippai, B., Takatsy, A., & Bock-Marquette, I
According to the Vitamin B12 is present in a range of foods, including: eggs poultry fish meat milk and other dairy products beef liver clams some fortified breakfast cereals and nutritional yeasts Dietary supplements are also available for those who do not consume enough vitamin B12 as part of their diet
The injections are typically more effective than supplements because supplements are absorbed through the digestive tract