There is no substantial evidence that vitamin B-12 injections help with weight loss as of June 2015, according to Mayo Clinic. Doctors typically prescribe injections of vitamin B-12, which occurs naturally in meat, fish, dairy products and other foods, to treat or prevent B-12 deficiency and pernicious anemia.
People who support vitamin B-12 injections for weight loss say the dosages produce more energy and boost the metabolism, which helps eliminate excess pounds. However, patients who do not have vitamin B-12 deficiencies generally do not receive energy boosts, notes Mayo Clinic. Doctors may prescribe the drug metformin to help Type 2 diabetes patients lose weight, and vitamin B-12 deficiency can be a side effect of the drug. Patients should consult their doctors before taking vitamin B-12 injections.