Vitamin B12

Vitamin B12 is used for treating vitamin B12 deficiency. It can also be used for energy and athletic performance.

Vitamin B12 Overview

Reviewed: July 15, 2014

B12 is a vitamin that is necessary for healthy blood and nerve cells and DNA formation.

Vitamin B12 is used most often for energy and athletic performance, decreasing the risk of heart disease, dementia, and for treating vitamin B12 deficiency.


Vitamin B12 has not been proven effective for all of the uses listed in this article. Vitamin B12 may be used for other conditions. Ask your doctor or pharmacist for more information.

Research has shown that vitamin B12 supplements (along with folic acid and vitamin B6) do not reduce the risk of getting heart disease. Scientists had thought that these vitamins might be helpful because they reduce blood levels of homocysteine, a compound linked to an increased risk of having a heart attack or stroke.


Older people that develop dementia often have high levels of homocysteine in the blood. Vitamin B12 (with folic acid and vitamin B6) can lower homocysteine levels, but scientists don't know yet whether these vitamins actually help prevent or treat dementia.


Advertisements often promote vitamin B12 supplements as a way to increase energy or endurance. Except in people with a vitamin B12 deficiency, no evidence shows that vitamin B12 supplements increase energy or improve athletic performance.

Vitamin B12 is used for treating vitamin B12 deficiency. 

Vitamin B12 deficiency causes tiredness, weakness, constipation, loss of appetite, weight loss, and megaloblastic anemia. Nerve problems, such as numbness and tingling in the hands and feet, can also occur. Other symptoms of vitamin B12 deficiency include problems with balance, depression, confusion, dementia, poor memory, and soreness of the mouth or tongue. Vitamin B12 deficiency can damage the nervous system even in people who don't have anemia, so it is important to treat a deficiency as soon as possible.

In infants, signs of a vitamin B12 deficiency include failure to thrive, problems with movement, delays in reaching the typical developmental milestones, and megaloblastic anemia.

Side Effects of Vitamin B12

There are no reported side effects of vitamin B12 consumption from food and supplements. 

This is not a complete list of vitamin B12 side effects. Ask your doctor or pharmacist for more information.

Tell your doctor if you have any side effect that bothers you or that does not go away.

Vitamin B12 Interactions

Tell your doctor about all the medicines you take, including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take:

  • Chloramphenicol
  • Proton pump inhibitors, such as omeprazole (Prilosec) and lansoprazole (Prevacid)
  • H2 receptor antagonists, such as cimetidine (Tagamet), famotidine (Pepcid), and ranitidine (Zantac)
  • Metformin 

This is not a complete list of vitamin B12 drug interactions. Ask your doctor or pharmacist for more information.

Vitamin B12 Precautions

Talk to your doctor or pharmacist before using vitamin B12 if you are pregnant, breast-feeding, or trying to become pregnant.