How Much Vitamin B12 Is Too Much?

Vitamin B12 is one of the 13 essential vitamins your body needs to work properly. As a result, it’s common to see it added to many foods — from cereal to your favorite energy drinks. It’s also available as a supplement and is included in most daily multivitamins. 

But how much vitamin B12 do you really need, and what happens if you take too much?

What is vitamin B12?

Vitamin B12, also called cobalamin, is one of the eight B vitamins your body needs to function properly. It’s considered an essential vitamin, which means your body can’t make it on its own. You need to get vitamin B12 from food or supplements. 

The benefits of vitamin B12 for your body include:

• Making red blood cells

• Protecting your nerves

• Making DNA

• Converting food into energy

• Regulating hormones

There are several different types of vitamin B12. The most common forms found in supplements include:

• Cyanocobalamin

• Hydroxycobalamin

• Adenosylcobalamin

• Methylcobalamin 

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There’s no evidence that your body absorbs any one form better than another.

Good to know: Vitamin B12 is mainly found in animal sources, not in plants. People who follow a vegetarian or vegan diet may not get enough vitamin B12 from their food.

How much vitamin B12 do you need each day?

The amount of vitamin B12 you need each day depends on your age. The recommended daily amounts of vitamin B12 are broken down in the chart below.

Can you take too much vitamin B12?

You can’t take too much Vitamin B12. It’s a water-soluble vitamin, which means you can easily get rid of extra amounts through your urine.

To be more specific, your body absorbs vitamin B12 mostly through a protein called intrinsic factor. This protein is made by cells in your stomach. It binds to vitamin B12 so your body can absorb it. But intrinsic factor can only bind to a small amount of vitamin B12 at a time. Any extra goes into your urine and leaves your body when you pee.

That being said, people with certain health conditions may experience side effects from taking vitamin B12. We cover that in more detail below.

How much vitamin B12 should you take?

Even though you can’t take too much vitamin B12, that doesn’t mean you need to take high doses.

EXPERT PICKS: WHAT TO READ NEXT

• What does vitamin B12 do for your body? Learn about the benefits of vitamin B12 and common foods that can help you meet your daily needs.

• Know the signs your B12 levels may be too low: This guide covers common symptoms of vitamin B12 deficiency and when to talk to a healthcare professional.

• Find the right dosage for supplements and prescriptions: We explain typical B12 dosages and the differences between oral and injectable forms.

If your vitamin B12 levels are low, a common recommended OTC dosage is about 1,000 mcg per day. Your healthcare team can tell you how much vitamin B12 you should take based on your current levels and health conditions.

The amount of vitamin B12 in OTC dietary supplements varies. It’s available as part of a multivitamin or as a supplement by itself. Typical vitamin B12 amounts include:

• Multivitamins: 5-25 mcg

• B-complex vitamins: 50-500 mcg

• Vitamin B12-only supplements: 500-5,000 mcg

Keep in mind: Oral tablets are the most common form of vitamin B12 supplement. But if you have a condition or are taking a medication that prevents your body from absorbing vitamin B12, an oral tablet likely won’t work for you. A dissolving tablet or liquid placed under your tongue may be a better option. These forms are absorbed in your mouth instead of your stomach.

How much vitamin B12 is in prescription forms?

If your vitamin B12 levels are very low, or if OTC supplements don’t work for you, your healthcare team may recommend a prescription form. There are three main types of prescription vitamin B12 products:

• Cyanocobalamin injection (Dodex): 1,000 mcg/mL

• Hydroxocobalamin injection: 1,000 mcg/mL

• Cyanocobalamin nasal spray (Nascobal): 500 mcg per spray

Your healthcare team will give you specific dosage instructions if you need prescription vitamin B12.

Are there risks or side effects from high doses of vitamin B12?

Because your body can’t absorb large amounts of B12, high doses usually don’t cause problems in most people. But, in rare cases, high doses of vitamin B12 can be a problem for people with certain health conditions.

Skin-related side effects

Some people have experienced skin-related side effects (like acne, rosacea, rash, or flushing) after getting high doses of vitamin B12 by injection. Examples of high doses include vitamin B12 intravenous (IV) infusions or muscle injections given more than once a week. 

Some injectable vitamin B12 products also contain iodine. Researchers think these skin reactions could be due to iodine rather than vitamin B12 itself. But they don’t know for sure. 

Skin-related effects seem to happen more often with hydroxocobalamin than cyanocobalamin. Oral vitamin B12 dietary supplements haven’t been connected to these side effects.

Increased cancer risk

This one is controversial and not confirmed. Some research has suggested that high doses of vitamin B12 may increase cancer risk. Other research shows a lower risk or no link at all. This potential link is included to make sure you have all the facts. But based on the current research, most people don’t need to worry that taking vitamin B12 will increase their cancer risk. 

Health condition-related risks

High doses of vitamin B12 aren’t an issue for most people. But people with the following health conditions may have a higher risk of serious side effects from vitamin B12:

• Megaloblastic anemia: In rare cases, high doses of vitamin B12 can cause low potassium levels and high platelet counts when used to treat this condition. Healthcare professionals monitor for these side effects. But let your team know if you have muscle cramps, confusion, or trouble breathing if you’re taking vitamin B12 for this condition. 

• Leber’s disease: This condition causes damage to the optic nerve and gets worse over time. Vitamin B12 in the form of cyanocobalamin can worsen damage to the optic nerve in people with Leber’s disease. A different form of vitamin B12 is usually recommended.

• Kidney problems: Prescription vitamin B12 injections contain small amounts of aluminum. Kidney problems can make it harder to remove aluminum from your body. Large amounts of aluminum are toxic, so it’s best to avoid large doses of injectable B12 if you have kidney problems.

These risks are mainly associated with large doses of prescription injectable vitamin B12 (cyanocobalamin). Your healthcare team will screen for these risks before prescribing vitamin B12. They’ll also watch out for any problems while you’re taking it. 

What’s the best way to get enough vitamin B12?

In most cases, your daily diet provides enough vitamin B12. Most adults and children get between 4 mcg and 6 mcg per day. Vitamin B12 in your diet comes from: 

• Animal sources, such as meat, fish, milk, and eggs

• Foods that have been fortified with vitamin B12, such as breakfast cereal and non-dairy milk (like almond or soy) 

If you need more vitamin B12 than your diet provides, supplements can help make up the difference.

Do you need a vitamin B12 supplement?

It’s best to talk to your healthcare team before taking any OTC vitamins or supplements. They can test your vitamin B12 levels. If your levels are low, they can help figure out why and recommend the right dose and form for you.

You’re more likely to have low vitamin B12 levels if you:

• Are age 65 or older

• Take metformin (Glucophage)

• Take oral contraceptive pills

• Take acid-reducers, such as omeprazole (Prilosec) or famotidine (Pepcid)

• Have health conditions that affect your stomach or bowels, such as celiac disease

• Have had weight-loss surgery

• Have had surgery on your small intestine

• Are vegetarian or vegan (or are an infant breastfed by someone who is vegetarian or vegan)

Vitamin B12 side effects

Vitamin B12 is well-tolerated and has few side effects. In clinical studies, prescription vitamin B12 caused the following side effects in a small number of people:

• Nausea

• Mild diarrhea

• Itchy skin

• Common cold-like symptoms

More severe side effects are also possible. Like any medication, vitamin B12 can cause allergic reactions in some people. Stop taking it and seek medical care if you develop a body rash, swelling of your mouth or lips, or trouble breathing after taking it.

Vitamin B12 can also rarely cause a condition called polycythemia vera, which causes your body to make too many red blood cells. Symptoms develop over time and can include itchy skin, fatigue, and dizziness. Let a healthcare professional know if these symptoms appear while you’re taking vitamin B12.

What should I do if I accidentally take too much vitamin B12?

If you or a loved one takes a large amount of vitamin B12, it’s not likely to be an issue. But it might put your mind at ease to contact a healthcare professional or call Poison Control at 1-800-222-1222 for guidance. If any symptoms seem concerning or life-threatening, seek emergency care right away. There could be something else going on that needs emergency treatment.

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Written by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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