Vitamin B12 Deficiency Harvard Health Struggling with B12 injection frequency? Here's what you need to know If you have Pernicious Anaemia (PA) or B12 deficiency due to autoimmune gastritis, NHS guidance is clear: You should B12 Shots: Vitamin B12 Injections Benefits, Uses, Risks Dr. Axe B12 Shots at Home: How, Where & How Often to Inject Yourself AZ IV Medics Vitamin B12 Deficiency Vitamin B12 deficiency happens when the body does not have enough vitamin B12. Vitamin B12 is important for making healthy red blood cells and keeping nerves