Can you take too much B12? Symptoms, side effects, and safety

Overview: What does too much B12 feel like?

Vitamin B12 is a water-soluble vitamin necessary for nervous system function, red blood cell production, and cell division. Most people get all the vitamin B12 the body needs from a healthy diet. Some people such as older adults, pregnant women, breastfeeding women, people on a vegan or vegetarian diet, or people taking medications known as metformin or a proton pump inhibitor (such as omeprazole) may need to take over-the-counter or prescription supplements to get enough vitamin B12. These supplements usually contain cyanocobalamin. People taking vitamin B12 supplements often take other supplements such as b complex, vitamin B9 (folate or folic acid), and vitamin B6 (pyridoxine). People with a serious B12 deficiency may need B12 intramuscular injections.

While other vitamins and minerals may be toxic at high doses, vitamin B12 is generally considered safe even at high doses. Excess vitamin B12 is eliminated in the urine, so taking too much B12 is simply spending money to flush it down the toilet. However, taking prescription levels of B12 doses may cause mild symptoms. 

RELATED: 9 common nutrient deficiencies in the U.S.

Common symptoms:

1. Skin issues:

   • Acne or rosacea-like rash.

   • Skin flushing or redness.

2. Gastrointestinal:

   • Nausea or vomiting.

   • Diarrhea.

3. Neurological:

   • Dizziness.

   • Tingling or numbness in hands and feet (peripheral neuropathy).

4. Fatigue or Weakness:

   • Feeling unusually tired or weak.

5. Anxiety or Mood Changes:

   • Restlessness.

   • Irritability or mood swings.

Rare but possible symptoms:

1. Elevated blood pressure or heart issues:

   • Increased heart rate or palpitations.

2. Allergic reactions:

   • Swelling, itching, or difficulty breathing (requires immediate medical attention).

3. High blood volume:

   • Excessive blood levels of B12 may mimic symptoms of polycythemia (headaches, redness, or blood clots).

4. Worsening of kidney function:

   • In individuals with pre-existing kidney disease, high doses might exacerbate the condition.

Causes of high B12 levels:

• High-dose B12 supplementation.

• Medical conditions like liver disease, leukemia, or kidney disease can elevate B12 levels without supplementation.

What to Do:

• Stop excessive supplementation if you're taking high doses without medical supervision.

• Consult a healthcare provider for blood tests to check B12 levels and rule out underlying conditions.

• Consider adjusting dietary intake if necessary (e.g., from fortified foods or animal products).

What are the signs of too much B12?

Most people who take too much vitamin B12 do not have symptoms. Signs of too much B12 are more likely in people taking prescription-level daily doses of 1,000 to 2,000 micrograms or more. Even then, side effects are unlikely. At prescription-strength doses, only about 1% of the vitamin B12 is absorbed into the bloodstream. Excess B12 in the blood is rapidly excreted through the urine. People are most likely to experience symptoms if they are being given B12 injections.

Possible early signs of too much B12 include:

• Pain

• Headache

• Mild diarrhea

• Nausea

• Itching

• Skin conditions such as: Acne or rosacea

For people taking megadoses of vitamin B12 supplements, severe symptoms are very rare and include:

• Heart palpitations

• Restlessness

• Anxiety

• Insomnia

• Facial redness

Vitamin B12 shots are more likely to cause problems. These include:

• Pain

• Headache

• Itching

• Skin rash

• Fever

• Shortness of breath

• Rapid weight gain

Other possible severe side effects of injectable vitamin B12 include:

• Low potassium

• Congestive heart failure

• Pulmonary edema

• Increase in platelets

• Blood clots

• Severe allergic reactions

RELATED: How to make sure you absorb your supplements

Too much vitamin B12 vs. vitamin B12 deficiency

Both too much vitamin B12 and too little vitamin B12 may have no symptoms. It’s hard to get too much vitamin B12 because it’s poorly absorbed at high doses and the body quickly eliminates it. That means that high B12 levels don’t last very long. Other than B12 supplementation, there are some medical causes of elevated B12 including: liver disease, leukemia, or kidney disease. Some people with low levels of vitamin B12 may have no symptoms or the symptoms may be subtle. When they do, many of the symptoms are similar to a vitamin B12 excess. The critical difference is this: a vitamin B12 deficiency primarily causes anemia, a shortage of red blood cells. The symptoms of anemia such as fatigue, feeling lightheaded or dizzy, pale skin, and yellowing of the skin are critical clues in the diagnosis of B12 deficiency.

RELATED: Vitamin B12 deficiency symptoms: what are the early signs of vitamin B12 deficiency?

When to see a doctor

Too much B12 does not commonly cause symptoms. When it does, they tend to be mild and not easily identified with any specific cause. 

If you are self-administering B12 supplements and have mild problems like headaches or tiredness, then consider cutting back on the amount of vitamin to the recommended daily allowance. If that doesn’t work, consider discontinuing the supplement. 

B12 injection side effects, however, are a different matter. They can cause serious side effects. When receiving injections, always report side effects to the healthcare professional overseeing treatment. 

Diagnosing too much B12 is not a critical task since the body clears B12 rapidly. If a healthcare provider suspects that too much B12 is an issue, you will probably be asked to quit taking supplements. Diagnosing B12 injection side effects is a critical task, particularly since some of the worst side effects, like heart failure, can occur early in treatment. For this reason, people receiving B12 shots are given regular blood tests to monitor B12 levels and other critical substances such as potassium.

Complications of too much B12

There are no complications associated with untreated high levels of B12 in the body. However, one study found that persistently high levels of vitamin B12 in older adults increased the risk of death from all causes independent of other risk factors. High vitamin B12 levels are also associated with a higher mortality rate in people on hemodialysis.

How to treat symptoms of too much B12

The standard treatment for too much B12 is to stop taking supplements or to reduce injection doses. There is no antidote if too much B12 is taken or injected, but B12 is not considered toxic or life-threatening. If too much B12 produces symptoms, the only options are symptom relief treatments and supportive care.

Sources

• Vitamin B12 health professional fact sheet, NIH Office of Dietary Supplements

• Vitamin B12 (cobalamin), StatPearls

• Vitamin B12 injection, Cleveland Clinic

• Vitamin B12 (cobalamin), StatPearls

• Association of plasma concentration of vitamin B12 with all-cause mortality in the general population in the Netherlands, Journal of the American Medical Association (JAMA)

• Association of serum vitamin B12 and folate in mortality in incident hemodialysis patients, Nephrology Dialysis Transplantation

• Toxicity induced by multiple high doses of vitamin B12 during pernicious anemia treatment: A case report, Clinical Toxicology