Vitamin B12 (cyanocobalamin) is a dietary supplement used to treat low blood vitamin B12 levels (vitamin B12 deficiency). It's available as a pill and liquid that's typically taken by mouth once per day. But depending on your specific situation, your provider might have you take a different dosage. Vitamin B12 (cyanocobalamin) is generally well tolerated and doesn't have many side effects.
Vitamin B12 deficiency in adults
Vitamin B12 (cyanocobalamin) is a dietary supplement. Your body needs vitamin B12 (cyanocobalamin) for several processes, such as promoting red blood cell growth, maintaining nerve cell health, and making DNA (genetic material).
Source: DailyMed
Side effects that you should report to your care team as soon as possible:
Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):
Can help restore vitamin B12 levels if you're not getting enough from your diet
Taken by mouth once per day
Available over the counter in many different forms (e.g., pill, gummy, liquid)
Not labeled for use in children younger than 18 years of age
Many different dosages available, which can be confusing
Some forms (e.g., liquids, gummies) contain sugar
Discuss with your provider whether you're getting enough vitamin B12 from your diet or if you should take a vitamin B12 (cyanocobalamin) supplement.
For the fast-dissolvable tablets, make sure your hands are dry before handling the medication. Place the tablet on the tongue to let it dissolve, and swallow with saliva. Don't swallow the fast-dissolving tablets whole. You don't need to drink water when taking a fast-dissolving tablet.
For the liquid, use the measuring device that's included in the packaging to measure your dose of vitamin B12 (cyanocobalamin). This can sometimes be a dropper, medication dose cup, or an oral syringe. Ask your pharmacy to provide you with one if the product doesn't include it in its packaging or if you lose it. Don't use household spoons because they might not be accurate and might cause you to take the wrong dose. Follow the directions on the product labeling or your provider's instructions.
You can take vitamin B12 (cyanocobalamin) with or without food. Check your product's labeling or with your provider for specific recommendations.
Vitamin B12 (cyanocobalamin) is found in many other multivitamins and supplements. Make sure to read labels carefully on all of the dietary supplements you're taking to see if it contains vitamin B12 (cyanocobalamin).
If you're taking metformin, a proton pump inhibitor (PPI) like omeprazole (Prilosec), or an H2 antagonist like famotidine (Pepcid AC), ask your provider whether you need to also take a vitamin B12 (cyanocobalamin) supplement. These medications can lower your blood vitamin B12 (cyanocobalamin) levels.
Keep vitamin B12 (cyanocobalamin) out of reach of children so that they don't accidentally take it. If your child accidentally took vitamin B12 (cyanocobalamin), call your local Poison Control Center right away at 1-800-222-1222.
Vitamin B12 (cyanocobalamin) can cause some serious health issues. This risk may be even higher for certain groups. If this worries you, talk to your doctor or pharmacist about other options.
Allergic reactions to vitamin B12 (cyanocobalamin) are possible, including life-threatening reactions like facial swelling, shock, and anaphylaxis (e.g., closing of the throat). If you notice difficulty breathing, a choking sensation, swelling around your eyes, swelling of the lips or tongue, dizziness, or nausea after using vitamin B12 (cyanocobalamin), get medical attention right away.
People with a rare, inherited eye condition called Leber's disease who received vitamin B12 developed severe eye damage. Vitamin B12 (cyanocobalamin) products isn't recommended in people with Leber's disease. If you have Leber's disease, speak with your provider about alternatives for vitamin B12 supplementation.
If you have pernicious anemia, discuss with your provider whether vitamin B12 (cyanocobalamin) supplements that are taken by mouth are right for you. Sometimes, treating severe pernicious anemia with vitamin B12 can cause serious problems, like low potassium and high platelet levels. If you do, your provider will follow up with you more often. They'll track your potassium and platelet levels through bloodwork during treatment with vitamin B12 (cyanocobalamin). Contact your provider if you notice headache, confusion, shortness of breath, heart palpitations (chest pounding), muscle weakness or cramps, or unusual bleeding. These can be symptoms of electrolyte or platelet problems.
Risk factors: Taking more than 10 mcg of vitamin B12 daily
Taking vitamin B12 can sometimes mask anemia due to low folic acid levels). This means that vitamin B12 might help raise your red blood cell count without affecting your folic acid (folate) levels (so your folic acid levels will still be low). Your provider will check your folic acid levels through bloodwork before you start vitamin B12 (cyanocobalamin) to make sure you receive appropriate treatment for all your nutrient deficiencies.
The typical dose ranges from 100 mcg to 5,000 mcg once a day (preferably with food).
Keep in mind that vitamin B12 (cyanocobalamin) is available in many different forms (e.g., oral tablets, orally dissolving tablets, gummies, lozenges). Vitamin B12 (cyanocobalamin) also comes in different strengths. For these reasons, each vitamin B12 (cyanocobalamin) supplement can have different directions on how to take.
Please read the manufacturer's label for directions that are specific to the vitamin B12 (cyanocobalamin) product you have or follow your provider's instructions. Your provider might recommend a dose of vitamin B12 (cyanocobalamin) that's different from the manufacturer's label.
Your provider might adjust your dose based on your vitamin B12 levels, whether you have medical conditions that cause lower vitamin B12 levels (e.g., Crohn's disease), or whether you're taking other medications that affect vitamin B12 levels.
Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. Tell your healthcare professional if you are taking any other prescription or nonprescription (over-the-counter [OTC]) medicine.
Vitamin B12 deficiency in adults
To maintain normal vitamin B12 levels in adults with pernicious anemia (low red blood cell count due to low vitamin B12) after receiving cyanocobalamin injection
To treat and prevent vitamin B12 deficiency in adults
Vitamin B12 deficiency, including with pernicious anemia
Schilling test (vitamin B12 absorption test) - not commonly used
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Allen, L. H. (2012). Vitamin B-12. Advances in Nutrition.
American Society of Hematology. (n.d.). Blood basics.
Ankar, A., et al. (2022). Vitamin B12 deficiency. StatPearls.
Calderón-Ospina, C. A., et al. (2020). B vitamins in the nervous system: Current knowledge of the biochemical modes of action and synergies of thiamine, pyridoxine, and cobalamin. Central Nervous System Neuroscience & Therapeutics.
Devalia, V., et al. (2014). Guidelines for the diagnosis and treatment of cobalamin and folate disorders. British Journal of Haemotology.
Gomollón, F., et al. (2017). Oral cyanocobalamin is effective in the treatment of vitamin B12 deficiency in Crohn's disease. Nutrients.
Marlex Pharmaceuticals Inc. (2020). B - 12- cyanocobalamin tablet [package insert]. DailyMed.
MedlinePlus. (2022). Folate-deficiency anemia.
Miller, J. W. (2018). Proton pump inhibitors, H2-receptor antagonists, metformin, and vitamin B-12 deficiency: Clinical implications. Advances in Nutrition.
National Heart, Lung, and Blood Institute. (2022). Thrombocythemia and thrombocytosis.
National Institutes of Health, Office of Dietary Supplements. (2021). Vitamin B12: Fact sheet for consumers.
National Institutes of Health, Office of Dietary Supplements. (2022). Vitamin B12: Fact sheet for health professionals.
National Organization for Rare Disorders. (2008). Anemia, pernicious.
Par Pharmaceutical, Inc. (2018). Nascobal- cyanocobalamin spray [package insert]. DailyMed.
Paul, C., et al. (2017). Comparative bioavailability and utilization of particular forms of B12 supplements with potential to mitigate B12-related genetic polymorphisms. Integrative Medicine.
Shemesh, A., et al. (2022). Leber hereditary optic neuropathy (LHON). StatPearls.
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