Vitamin B12 is an essential vitamin. If you don't get enough B12 in your diet or have a medical condition that makes it difficult for your body to absorb B12 from foods, you might develop B12-deficiency anemia. Intramuscular B12 injections may help treat B12 deficiency anemia and its symptoms, such as fatigue and depression; however, B12 injections do not provide the same benefits for everyone. Talk to your doctor before using B12 supplements or injections.
Your vitamin B12 shots may not be working for many reasons, most related to why you're taking them in the first place, whether for a deficiency or the purported health benefits.
B12 for Anemia
Vitamin B12 anemia develops from a deficiency of the vitamin, leading to a reduction in red blood cell count. In the treatment of B12-deficiency anemia, B12 injections are typically administered on a monthly basis, or as often as once-a-week at the beginning of treatment, according to MedlinePlus. However, B12 injections are only given if you're unable to absorb the vitamin from food or through a supplement. While B12 injections are usually effective in treating B12 deficiency anemia, if the B12 deficiency progresses to a more severe condition called pernicious anemia, complications of the deficiency may persist despite treatment with B12 injections. According to MedlinePlus, if B12 replacement does not start within six months of when symptoms begin, nerve damage caused by pernicious anemia may be permanent.
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B12 for Energy
Some people take B12 injections for more energy. It's important to note, however, that if you don't have B12 deficiency, B12 injections will not increase your energy levels or provide any other benefits. B12 is a water-soluble vitamin, which means that excess amounts obtained from unnecessary supplementation will be flushed from the body. While a B12 deficiency may cause fatigue, so can other health problems and deficiencies of other nutrients, such as iron. A CBC test or serum B12 level test can verify whether you have low energy that may be remedied with B12 injections.
B12 for Weight Loss
Some weight-loss clinics offer B12 injections. Proponents of B12 for weight loss claim that B12 injections aid weight-control efforts by boosting your metabolism and giving you more energy to engage in exercise. Nevertheless, like using B12 to increase energy, there is no evidence that B12 shots will help you lose weight or offer metabolic advantages in the absence of a B12 deficiency, according to Mayo Clinic nutritionist Katherine Zeratsky, R.D., L.D. While easy fixes for weight loss may sound tempting, time-tested diet and exercise are the only surefire safe and effective weight-loss remedies.
Conditions Affecting B12 Absorption
B12 replacement with injections or other forms of supplementation may be less effective in people with conditions that affect B12 absorption. In addition to pernicious anemia, other conditions that can inhibit B12 absorption include chronic alcoholism, Crohn's disease, celiac disease and parasitic infections. While B12 absorption problems may sometimes be "cured" with short-term B12 injection therapy — once the underlying condition causing the malabsorption is properly treated — some people may require lifelong monthly B12 shots, according to MedlinePlus.