Skip to Content

Vitamin B12

Generic Name: cyanocobalamin (oral) (sye AN oh koe BAL a min)
Brand Name: B-12, Eligen B12, Vitamin B12

Medically reviewed on July 16, 2018

What is oral Vitamin B12?

Vitamin B12 is a man-made form of vitamin B12. Vitamin B12 is important for growth, cell reproduction, blood formation, and protein and tissue synthesis.

Vitamin B12 is used to treat vitamin B12 deficiency in people with pernicious anemia and other conditions.

Vitamin B12 may also be used for purposes not listed in this medication guide.

Important Information

You should not use Vitamin B12 if you are allergic to cobalt, or if you have Leber's disease.

Before taking this medicine

You should not use this medicine if you are allergic to cobalt, or if you have Leber's disease. Vitamin B12 can lead to optic nerve damage (and possibly blindness) in people with Leber's disease.

Tell your doctor if you have ever had:

  • heart disease;

  • diabetes;

  • a bleeding or blood clotting disorder;

  • gout;

  • an iron or folic acid deficiency;

  • low levels of potassium in your blood; or

  • an intestinal disorder such as ulcerative colitis.

Tell your doctor if you are pregnant or breast-feeding.

Do not give this medicine to a child without medical advice.

How should I take oral Vitamin B12?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Carefully follow instructions about whether to take your Vitamin B12 with or without food.

Your dose needs may change if you become pregnant, if you breast-feed, or if you eat a vegetarian diet. Tell your doctor about any changes in your diet or medical condition.

Do not swallow a lozenge or sublingual tablet whole. Allow it to dissolve in your mouth without chewing. The sublingual tablet should be placed under your tongue.

Do not crush, chew, or break an extended-release tablet. Swallow it whole with a full glass of water.

You may need frequent medical tests to help your doctor determine how long to treat you with Vitamin B12.

To treat pernicious anemia, you will have to use Vitamin B12 on a regular basis for the rest of your life. Not using the medication can lead to irreversible nerve damage in your spinal cord.

Pernicious anemia is also treated with folic acid to help maintain red blood cells. However, folic acid will not treat Vitamin B12 deficiency and will not prevent possible damage to the spinal cord. Take all of your medications as directed.

Store at room temperature away from moisture, heat, and light.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while taking oral Vitamin B12?

Avoid drinking large amounts of alcohol. Heavy drinking can make it harder for your body to absorb Vitamin B12.

Oral Vitamin B12 side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have:

  • shortness of breath (even with mild exertion), swelling, rapid weight gain;

  • cough, chest pain; or

  • low potassium level--leg cramps, constipation, irregular heartbeats, fluttering in your chest, increased thirst or urination, numbness or tingling, muscle weakness or limp feeling.

Common side effects may include diarrhea.

  • diarrhea;

  • numbness or tingling;

  • fever;

  • joint pain;

  • swollen tongue; or

  • itching or rash.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: Side effects (in more detail)

What other drugs will affect oral Vitamin B12?

Tell your doctor about all your other medicines, especially:

This list is not complete. Other drugs may affect Vitamin B12, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Hide