Symptoms of taking too much vitamin B12 have been reported in very limited situations, but most experts report that the supplement is safe even at high doses. For this reason, the U.S. Food and Drug Administration (FDA) lists vitamin B12 in the Generally Recognized as Safe (GRAS) category and has not set an upper dosage limit.
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Can Too Much B12 Cause Symptoms?
Since taking B12 in high doses has not been seen to negatively affect people in any way, there are no known symptoms associated with high levels of the vitamin. The water-soluble vitamin is expelled from the body before it has the chance to cause any issues.
However, a few limited studies have raised concerns about the possible side effects of taking vitamin B12:
A 2019 study found that taking more than 25 micrograms (mcg) per day or higher was associated with an increased risk of bone fractures in postmenopausal women.
A study conducted in the Netherlands found that higher blood levels of vitamin B12 were associated with a higher risk of all-cause mortality (death from any cause). Study authors included people taking B12 supplements, except those who were taking injectable B12 supplements. They concluded that “caution should be taken when considering vitamin B12Â supplementation in the absence of a vitamin B12Â deficiency.”Researchers found that combined supplementation of folic acid, vitamin B6, and vitamin B12Â was associated with poor renal function and an increase in vascular events in patients with diabetic nephropathy.
Synthetic B12 Side Effects
There have been some reports of reactions to synthetic forms of vitamin B12.
For instance, A 2020 case report showed that a woman taking 1 milligram per day of cyanocobalamin (a synthetic form of vitamin B12) experienced acne, heart palpitations, anxiety, severe restlessness, facial ruddiness, headache, and insomnia. The symptoms went away after she stopped taking the supplement for two weeks.
And even though hydroxocobalamin (another synthetic form of B12) is generally well-tolerated, this prescription form of injectable B12 has been associated with certain side effects such as:
NauseaVomitingDiarrheaHeadachesDizzinessHot flushesPain or redness at the injection site
There have also been some reported reactions in people who are sensitive to hydroxocobalamin. These side effects may include:
RashItchingFeverNauseaDizzinessRigorsHot flushes
In rare cases, anaphylaxis may occur. Anaphylaxis is a life-threatening reaction that can cause rashes, hives, or difficulty breathing.
How Much B12 Is Too Much?
When looking at vitamin B12 levels, it’s difficult to say how much is too much. The vitamin is water-soluble, meaning it’s generally safe at high levels because the body flushes out what it doesn’t use with water.
To reap the benefits of B12 within the body, you’ll have to get enough of the essential nutrient. The amount of B12 a person needs depends on their age and pregnancy status, and can be broken down as follows:
Children 1–3: 0.9 microgram (mcg)/dayChildren 4–8: 1.2 mcg/dayChildren 9–13: 1.8 mcg/dayTeens 14–18: 2.4 mcg/dayAdults: 2.4 mcg/dayPregnant people: 2.6 mcg/dayPeople who are breastfeeding: 2.8 mcg/day
While these are general recommendations, some people may need more than others based on several factors, including:
Diet
Certain medications
Difficulty absorbing B12 into the body
Age (older adults may need more)
People with certain health disorders, such as gastrointestinal disorders, autoimmune diseases, and anemia
People who have had stomach or intestinal surgery
People in the above-mentioned groups may need more than the daily recommended allowance, but those in the general population do not, and taking more vitamin B12 than you need is unnecessary.
Many studies have investigated high doses of B12 to see how it affects the body, and none have determined a specific amount that could lead to an overdose.
Taking B12 in Excess
While no known adverse health effects are associated with taking too much B12, you’re wasting money if you supplement with the vitamin when you don’t need to. Your body will use what it needs and then expel the rest.
Does Vitamin B12 Interact With Any Medications?
There are some ways in which vitamin B12 interacts with certain medications. While taking a vitamin B12 supplement may not affect the medication’s effectiveness, the medication may affect your vitamin B12 levels.
Gastric acid inhibitors: Medications such as omeprazole (Prilosec), lansoprazole (Prevacid), and cimetidine (Tagamet) can interfere with your body’s ability to absorb vitamin B12.Metformin: This medication, used to treat diabetes, has been shown to reduce the absorption of vitamin B12 in the body and lower serum vitamin B12 concentrations in the blood.Colchicine: This medication is used to prevent or treat gout flares in certain patients and may inhibit vitamin B12 absorption, leading to a vitamin B12 deficiency.
If you are taking one of these medications, talk to your healthcare provider about whether you should take a vitamin B12 supplement or increase your intake of vitamin B12 foods, such as beef liver, clams, or nutritional yeast.
What Benefits Can Vitamin B12 Provide?
There are several benefits associated with B12, whether through diet or supplementation. They include:
Red blood cell formation: Red blood cells are vital for carrying oxygen throughout the body, so getting enough vitamin B12 can ensure this process runs smoothly.
Bone health: Your bones use vitamin B12 to help maintain bone mineral density, and a deficiency over time can lead to weaker bones and an increased risk of fractures.
Keeps eyes healthy: B12 deficiencies may lead to eye disease, including macular degeneration, so getting enough is crucial.Â
Mental health: Studies have shown that vitamin B12 plays a role in mood regulation and disorders, such as depression. Getting enough vitamin B12 can help improve mood and reduce symptoms of depression because of how it helps to synthesize and metabolize serotonin.
Brain health: B12 vitamins also help to maintain brain health by preventing the loss of neurons.Â
Energy and metabolism: Your energy levels and metabolism are vital to your overall health, and getting enough vitamin B12 helps to maintain the proper metabolic functioning so that your energy levels are at optimal levels.
Heart health: Several amino acids in the body play a role in heart health, including homocysteine. Homocysteine has been shown to increase the risk of heart disease if levels are too high. Vitamin B12 can keep levels of the amino acids where they need to be, mitigating that risk.
Skin, hair, and nail health: B12 promotes healthy cells within the body, including skin, hair, and nails.Â
Healthy pregnancy: Vitamin B12 helps with fetal development. Deficiencies in vitamin B12 also increase the risk of significant congenital abnormalities and birth defects, so getting enough is vital. Pregnant people should aim to get at least 2.6 mcg/day to ensure that they and the fetus are getting enough of this essential nutrient during pregnancy.
In the United States, the Food and Drug Administration (FDA) does not regulate dietary supplements the way it regulates prescription medications. As a result, some supplement products may not contain the ingredients listed on the label. When choosing a supplement, look for products independently tested or certified by organizations such as the National Sanitation Foundation (NSF), United States Pharmacopeia (USP), or ConsumerLab. For personalized guidance, consult your healthcare provider, registered dietitian nutritionist (RD or RDN), or pharmacist.
Key Takeaways
There is no clinical evidence of side effects from taking too much vitamin B12. However, there are reports of side effects from taking synthetic (injectable) forms of the vitamin which are available only by prescription.Vitamin B12 is water soluble, so anything the body doesn’t use is expelled through the urine. Some people may need more vitamin B12 than is generally recommended, including those with gastrointestinal disorders, autoimmune diseases, or anemia.
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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