Vitamin B12 is a water-soluble vitamin that plays a vital role in brain function and red blood cell production. Also known as cobalamin, it’s part of the B Complex. Deficiency in Vitamin B-12 is common, particularly in people who follow a vegan or vegetarian diet. The good news is that you can take Vitamin B-12 supplements in oral and injectable forms. B-12 shots are the most common, fast, and efficient way to replenish this vital nutrient in your body.