Generic name: cyanocobalamin (injection) [ sye-AN-oh-koe-BAL-a-min ]
Brand names: Vitamin B12, Vitamin B-12
Drug class: Vitamins

Medically reviewed by Drugs.com on Nov 26, 2024. Written by Cerner Multum.

What is Vitamin B12 ?

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.

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.

Vitamin B12 may cause serious side effects. Call your doctor at once if you have:

• heart problems--swelling, rapid weight gain, feeling short of breath;

• fluid build-up in or around the lungs--pain when you breathe, feeling short of breath while lying down, wheezing, gasping for breath, cough with foamy mucus, cold and clammy skin, anxiety, rapid heartbeats; 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 of Vitamin B12 may include:

• diarrhea; or

• swelling anywhere in your body.

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.

Related/similar drugs

Warnings

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 Vitamin B12 or cobalt, or if you have Leber's disease (an inherited form of vision loss). This medicine can lead to optic nerve damage (and possibly blindness) in people with Leber's disease.

Tell your doctor if you have ever had:

• eye problems or Leber's disease (in you or a family member);

• kidney or liver disease;

• iron or folic acid deficiency;

• any type of infection; or

• if you are receiving any medication or treatment that affects bone marrow.

Tell your doctor if you are pregnant or breastfeeding. Your dose needs may be different during pregnancy or while you are nursing.

How is Vitamin B12 given?

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

Vitamin B12 is injected into a muscle or under the skin. A healthcare provider may teach you how to properly use the medication by yourself.

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

Always follow directions on the medicine label about giving Vitamin B12 to a child. Your child's dose will depend on age, weight, diet, and other factors.

For pernicious anemia, you may have to use Vitamin B12 for the rest of your life. Do not stop using the medicine unless your doctor tells you to. Untreated vitamin B12 deficiency can lead to anemia or irreversible nerve damage.

Pernicious anemia is also treated with folic acid to help maintain red blood cells. Folic acid alone will not treat Vitamin B12 deficiency or prevent possible damage to the spinal cord. Use all medications as directed.

You will need frequent medical tests.

Vitamin B12 can affect the results of certain medical tests. Tell any doctor who treats you that you are using Vitamin B12.

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

Use a needle and syringe only once and then place them in a puncture-proof "sharps" container. Follow state or local laws about how to dispose of this container. Keep it out of the reach of children and pets.

What happens if I miss a dose?

Call your doctor for instructions if you miss a dose.

Get your prescription refilled before you run out of medicine completely.

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 using Vitamin B12?

Avoid drinking large amounts of alcohol while you are being treated with Vitamin B12.

What other drugs will affect Vitamin B12?

Other drugs may affect Vitamin B12, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

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.

Medical Disclaimer

Copyright 1996-2025 Cerner Multum, Inc. Version: 3.01.