Methylcobalamin (or tydroxycobalamin) is a man-made form of vitamin B12 used to treat deficiency of this vitamin. B12 helps your body use fat and carbohydrates for energy and make new protein. It is also important for normal red blood cells and nerves. Most people get enough vitamin B12 in their diet, but a deficiency may occur in people over 50 or with certain health conditions like poor nutrition or intestinal problems, low stomach acid, infection, or cancer. Serious vitamin B12 deficiency may result in anemia, fatigue, or nerve problems.