Vitamin B12 is an essential vitamin found in foods such as meat, fish, and dairy. It can also be made in a lab.

Vitamin B12 is required for the function and development of many parts of the body, including the brain, nerves, and blood cells. Methylcobalamin is the active form of vitamin B12. Cyanocobalamin, which must be processed by the body into the active form, is the most common type used in supplements.

People commonly use vitamin B12 for vitamin B12 deficiency, cyanide poisoning, and high levels of homocysteine in the blood. It is also used for canker sores, cataracts, Alzheimer disease, osteoporosis, fatigue, and many other conditions.