How do you feel if you have too much B12 in your system?

January 6, 2026 •

4 min read

As a water-soluble vitamin, B12 is generally considered safe, with excess amounts excreted through urine, which is why a true overdose is exceptionally rare. However, taking very high doses, especially through supplements or injections, can still lead to some unpleasant side effects.

Quick Summary

Excessive B12 intake can cause mild symptoms like acne, nausea, and headaches, though permanent damage is unlikely. Persistent high levels may indicate an underlying medical issue, not just supplementation.

Key Points

Rare Toxicity: B12 is water-soluble, meaning your body excretes excess amounts, making an overdose from food nearly impossible.
Supplemental Side Effects: High doses from supplements or injections can cause mild side effects like acne, nausea, and headaches.
Underlying Condition Indicator: Persistently high B12 levels may indicate an underlying issue, such as liver or kidney disease, rather than just supplement intake.
Paradoxical Symptoms: Some side effects of high B12, like tingling, can resemble symptoms of a deficiency, complicating self-diagnosis.
Professional Consultation: It is essential to consult a healthcare provider to determine the cause of elevated B12 and manage any symptoms.

Understanding Excess B12: What Does 'Too Much' Mean?

When your body has too much B12, the condition is known as hypercobalaminemia. It's crucial to distinguish between high B12 from diet and high B12 from supplements or underlying health conditions. Getting too much B12 from food alone is nearly impossible for most people. Because B12 is water-soluble, your body is very efficient at flushing out what it doesn't need. However, the story changes with high-dose supplementation, particularly injections, where side effects are more commonly reported.

Common Symptoms of High B12

While many people experience no symptoms with elevated B12, some individuals may encounter a range of effects when exposed to high levels, often from supplementation. These symptoms can be uncomfortable but are generally not life-threatening and typically resolve once the dosage is reduced. The most frequently reported symptoms include:

Skin problems: A notable side effect is the development of skin issues such as acne, rosacea, and general facial redness. Some individuals may also experience itching or rashes.
Gastrointestinal issues: Nausea, vomiting, and diarrhea are common digestive complaints associated with high B12 intake. Abdominal pain and bloating have also been reported.
Headaches and dizziness: A persistent headache or a sensation of dizziness can occur in some individuals taking high-dose supplements or injections.
Mood and anxiety: Increased anxiety and restlessness (akathisia) are documented side effects. In some rare cases, it has even been linked to more complex mood disturbances.
Neurological effects: A tingling or prickling sensation in the hands and feet (paresthesia) is a known symptom, though it is more typically associated with deficiency. Muscle weakness or cramps might also occur.
Cardiovascular symptoms: Some people have reported heart palpitations and high blood pressure with excessive B12.
Insomnia: Sleep disturbances and insomnia can occur, leaving individuals feeling tired despite being restless.

Potential Causes of High B12 Levels

For most people, high B12 levels are a result of taking supplements or receiving injections. However, in some cases, a high reading on a blood test can be a crucial indicator of an underlying health problem, and not just a benign side effect of supplementation.

High B12 levels from non-supplement sources may point to:

Liver disease: Conditions affecting the liver, such as cirrhosis or hepatitis, can cause B12 to accumulate in the bloodstream.
Kidney disorders: Since the kidneys excrete excess B12, impaired kidney function can lead to elevated levels.
Blood disorders: Certain types of leukemia or other myeloproliferative disorders can lead to high B12 levels.
Other conditions: Inflammatory diseases and certain types of cancer have also been associated with elevated B12.

High B12 vs. Deficiency Symptoms: A Comparison

Some symptoms of high B12 can paradoxically resemble symptoms of a deficiency, making proper diagnosis from a healthcare provider essential. This table helps illustrate some of the differences.


Symptom	High B12 (Hypercobalaminemia)	B12 Deficiency (Hypocobalaminemia)
Energy	Often accompanied by restlessness, anxiety, or insomnia.	Classic symptom is persistent fatigue, weakness, and tiredness.
Skin	Acne, rosacea, or facial redness may occur.	Can cause pale skin and hyperpigmentation.
Mood	Reported anxiety and restlessness.	Depression and irritability are common.
Headaches	Can be a frequent and unpleasant symptom.	Also a known symptom, often linked to anemia.
Tingling	Rarely, paresthesia can occur with high doses.	A very common and defining symptom (pins and needles).

What to Do If You Think Your B12 is Too High

If you suspect your B12 levels are too high, the first step is to consult with a healthcare professional, especially if you are experiencing persistent or concerning symptoms. They can order a blood test to confirm your B12 levels and help determine the underlying cause. If the high levels are due to supplementation, the doctor will likely advise you to stop or reduce your intake. It is crucial not to self-diagnose or alter your medication without professional guidance.

Conclusion

While a true overdose of vitamin B12 is extremely rare due to its water-soluble nature, excessive intake from supplements or injections can lead to a variety of uncomfortable side effects, including skin issues, gastrointestinal problems, and anxiety. It is important to note that persistently high B12 levels on a blood test can also be a significant warning sign for a more serious, underlying medical condition, such as liver or kidney disease. If you are concerned about how you feel if you have too much B12 in your system, seeking medical advice is the most prudent course of action to ensure your symptoms are properly evaluated and managed.

For more information on vitamin B12, consult the NIH Office of Dietary Supplements.(https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/)

Frequently Asked Questions

No, it is virtually impossible to overdose on vitamin B12 from dietary sources. Your body only absorbs a small percentage of B12 from food at a time and excretes the rest.

Skin issues, such as acne, rosacea, and facial redness, are among the most frequently reported side effects when taking high doses of B12 supplements.

While it can be harmless, persistently high B12 levels can sometimes signal an underlying medical condition like liver disease, kidney problems, or blood disorders. It's best to consult a doctor for a proper evaluation.

If you experience uncomfortable side effects from your supplement, stop taking it and talk to your healthcare provider. They can advise you on adjusting your dosage or discontinuing use.

Yes, side effects are more commonly reported with high-dose B12 injections than with oral supplements, as the body can absorb more of the vitamin more quickly.

High B12 levels from supplements are not known to cause permanent harmful effects and symptoms typically resolve after reducing intake. However, if an underlying medical condition is the cause, that condition needs treatment.

Yes, high doses of vitamin B12 can sometimes mask a folate deficiency, which is another B vitamin important for neurological health. A doctor can help ensure a proper balance.