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  • Writer's pictureShruti GOCHHWAL

Methylcobalamin (Vitamin B12): Uses, Side Effects and Warnings

Methylcobalamin is used to treat vitamin B12 deficiency. Vitamin B12 is important for the brain and nerves, and for the production of red blood cells. Methylcobalamin is sometimes used in people with pernicious anemia, diabetes, and other conditions. Methylcobalamin may also be used for purposes not listed in this medication guide.

Uses & Effectiveness

vitamin b12

medicine bottle

  1. A rare inherited condition marked by vitamin B12 deficiency (Imerslund-Grasbeck disease). Injecting vitamin B12 as a shot for 10 days followed by monthly injections for the remainder of life is effective for treating people with an inherited disease that results in poor absorption of vitamin B12.

  2. Vitamin B12 deficiency. Vitamin B12 can treat and prevent vitamin B12 deficiency. It can be taken by mouth, as a shot, or through the nose. The shot works best in people with severe vitamin B12 deficiency or associated nerve damage.

  3. Cyanide poisoning. Administering hydroxocobalamin (Cyanokit), a natural form of vitamin B12, as a shot for a total dose of up to 10 grams is likely an effective treatment for cyanide poisoning. Treatment of cyanide poising with hydroxocobalamin (Cyanokit) has been approved by the U.S. Food and Drug Administration (FDA).

  4. High levels of homocysteine in the blood (hyperhomocysteinemia). Taking vitamin B12 by mouth, along with folic acid and sometimes pyridoxine (vitamin B6), can lower blood levels of homocysteine.

  5. An eye disease that leads to vision loss in older adults (age-related macular degeneration or AMD). Some research shows that taking vitamin B12 with other B vitamins, including folic acid and vitamin B6, might help prevent an eye disease called age-related macular degeneration. But the effects of vitamin B12 alone on AMD are not clear.

  6. Canker sores. Using an ointment containing vitamin B12 helps to reduce pain of canker sores. Also, early research shows that taking vitamin B12 1000 mcg under the tongue (sublingually) might help to reduce the number of canker sore outbreaks, the duration of outbreaks, and pain caused by the canker sores.

Side Effects & Safety


person taking medicine

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

Common side effects may include:

  1. nausea, vomiting, diarrhea

  2. loss of appetite;

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.


For vitamin B12 deficiency: Vitamin B12 doses of 300-10,000 mcg daily have been used. However, some evidence suggests that the most effective oral dose is between 647-1032 mcg daily




Before taking this medicine

  1. You should not use methylcobalamin if you are allergic to vitamin B12 or cobalt.

  2. Tell your doctor if you have ever had Leber’s disease or other form of optic nerve damage;

  3. an iron or folic acid deficiency; or

  4. low levels of potassium in your blood.

  5. Tell your doctor if you are pregnant or breastfeeding.

  6. Do not give methylcobalamin to a child without medical advice.

What other drugs will affect methylcobalamin?

affect of methylcobalamin


Tell your doctor about all your other medicines, especially:

  1. chloramphenicol;

  2. colchicine

  3. antibiotic medicine;

  4. oral diabetes medicine that contains metformin; or

  5. medicines that reduce stomach acid, such as cimetidine, omeprazole, lansoprazole, Nexium, Prevacid, Prilosec, Zantac, and others.


How should I use methylcobalamin?

Use exactly as directed on the label, or as prescribed by your doctor. Methylcobalamin oral is taken by mouth. Methylcobalamin injection is injected into a muscle, usually 1 to 3 times per week. A healthcare provider can teach you how to properly use the medication by yourself.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you don’t understand all instructions. Do not swallow a lozenge, disintegrating tablet, or sublingual tablet whole. Allow it to dissolve in your mouth without chewing. The sublingual tablet should be placed under your tongue.

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. Store at room temperature away from moisture and heat.

What happens if I miss a dose?

Use the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not use 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 methylcobalamin?

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

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