Understanding Vitamin B12 Deficiency in Cancer Patients Are you feeling run down? Low Energy? A quick Vitamin B12 injection can help support energy, metabolism, and overall wellness. It delivers the vitamin directly into the muscle, allowing your body to B12 deficiency can cause mood swings, difficulty concentrating, pale skin, compromised immune system, infertility, fatigue, hair loss and so much more. If you are vegetarian or vegan, you may be B12 Injection Frequency: How Often Should You Get a B12 Shot? Liv Hospital