Can vitamin B12 cause ulcers?

January 8, 2026 •

4 min read

While a deficiency in vitamin B12 is a known cause of painful mouth ulcers, the myth that this vitamin can cause stomach ulcers is widely misunderstood. This article clarifies the distinction, explores the actual causes of different types of ulcers, and discusses the potential gastrointestinal side effects associated with B12 supplementation.

Quick Summary

Vitamin B12 is not a cause of stomach ulcers, which are typically caused by H. pylori bacteria or NSAID use. However, a B12 deficiency can cause mouth sores, and high doses of oral supplements may lead to mild GI upset like nausea or diarrhea.

Key Points

B12 Deficiency Causes Mouth Ulcers: Low levels of vitamin B12, not high levels, can cause painful canker sores or mouth ulcers.
B12 Does Not Cause Stomach Ulcers: Stomach ulcers are primarily caused by H. pylori bacteria or long-term use of NSAID pain relievers, not B12 intake.
Ulcer Medications Affect B12 Absorption: Long-term use of acid-reducing drugs (PPIs) to treat stomach ulcers can impair B12 absorption, leading to a deficiency.
B12 Supplements May Cause Mild GI Upset: High-dose oral B12 can sometimes cause mild digestive side effects like nausea or diarrhea, but this is different from an ulcer.
An H. pylori Infection Links Both Issues: An H. pylori infection can cause both stomach ulcers and a B12 deficiency, creating a misleading association between the two.
Consult a Doctor for Persistent Pain: Persistent stomach pain or severe GI issues should be professionally diagnosed to rule out serious causes like peptic ulcers.
Alternative Supplement Options Exist: If oral B12 causes stomach irritation, sublingual or injected forms can provide B12 without affecting the stomach.

Debunking the Myth: Vitamin B12 and Ulcers

The short and clear answer to "Can vitamin B12 cause ulcers?" is no, it does not cause stomach or peptic ulcers. This common misconception likely stems from confusing different types of ulcers and the complex relationship between vitamin B12 and the digestive system. While a deficiency in this essential vitamin can lead to painful mouth ulcers, it is not responsible for the deeper, more serious sores found in the stomach lining.

The Real Connection: Deficiency and Mouth Sores

Far from causing ulcers, a deficiency in vitamin B12 is actually a documented cause of recurrent aphthous stomatitis, or mouth ulcers.

Role of Vitamin B12: Vitamin B12 is crucial for the formation of red blood cells and the health of the nervous system. When a deficiency occurs, it can affect the mucous membranes lining the mouth, making them more susceptible to forming painful sores.
Other Deficiency Symptoms: Mouth ulcers often appear alongside other symptoms of B12 deficiency, such as extreme fatigue, a sore or red tongue (glossitis), and neurological issues like pins and needles.

High-Dose B12 and Potential GI Upset

Another source of confusion might be the mild gastrointestinal side effects associated with high-dose vitamin B12 supplements.

Side Effects of Excess B12: When taken in high doses, oral vitamin B12 supplements can sometimes cause digestive disturbances, including nausea, vomiting, and mild diarrhea.
Difference from Ulcers: These symptoms represent irritation, not the formation of an open sore or ulcer. For individuals experiencing stomach upset from supplements, alternatives like sublingual drops or injections may be better tolerated.

The True Causes of Stomach Ulcers

Stomach ulcers are primarily caused by factors unrelated to vitamin B12 intake. The two most common culprits are bacterial infection and the use of certain medications.

Helicobacter pylori (H. pylori): This bacterium is the most common cause of peptic ulcers worldwide. It can inflame and damage the protective lining of the stomach, allowing stomach acid to create a sore. A fascinating inverse relationship exists here, as H. pylori infection can also lead to B12 malabsorption and subsequent deficiency.
Nonsteroidal Anti-Inflammatory Drugs (NSAIDs): Long-term and frequent use of NSAIDs, such as aspirin and ibuprofen, can also erode the stomach lining and cause ulcers.

The Medication Link: Ulcer Treatment Can Cause B12 Deficiency

In a crucial twist, some medications used to treat peptic ulcers can actually lead to a vitamin B12 deficiency. Drugs known as Proton Pump Inhibitors (PPIs) and histamine antagonists (H2RAs) reduce stomach acid production. Stomach acid is essential for freeing vitamin B12 from the food it's bound to, initiating the absorption process. Long-term use of these medications can therefore impair B12 absorption. This scenario shows that ulcer medication can contribute to B12 deficiency, not the other way around. For more information on the link between these medications and B12 levels, the NIH provides a detailed fact sheet.

Mouth Ulcers vs. Stomach Ulcers: A Comparison


Feature	Mouth Ulcer (Aphthous Stomatitis)	Stomach (Peptic) Ulcer
Associated with B12	Yes, caused by deficiency.	No, not caused by B12 intake.
Primary Causes	Vitamin deficiencies (B12, iron, folate), stress, hormonal changes, genetics.	H. pylori bacteria and long-term NSAID use.
Location	Inside the cheeks, lips, tongue, or on the gums.	In the lining of the stomach or duodenum.
Appearance	Small, round, or oval lesions with a red halo and a white or yellowish center.	Open sores in the stomach lining, often associated with a burning sensation.
Symptoms	Painful sores that make eating and speaking uncomfortable.	Burning stomach pain, indigestion, nausea, bloating, and potential bleeding.

What to Do If You Experience Stomach Issues

If you are taking oral vitamin B12 supplements and experience stomach irritation, there are several steps you can take:

Take with Food: Taking the supplement with a meal can help reduce irritation to the stomach lining.
Split the Dose: If taking a high-dose supplement, splitting it into smaller, more frequent doses throughout the day can help.
Switch Formulations: Consider switching from an oral tablet to a sublingual (under the tongue) form, which bypasses the stomach, or discuss intramuscular injections with your doctor.
Consult a Healthcare Provider: Persistent or severe stomach pain should always be evaluated by a medical professional to rule out more serious causes, such as a peptic ulcer. They can determine the cause of your symptoms and ensure you are meeting your B12 needs safely.

Conclusion

The idea that vitamin B12 can cause ulcers is a misunderstanding. The relationship is far more nuanced: a deficiency of B12 can cause mouth sores, and medication for stomach ulcers can cause a B12 deficiency. The leading causes of stomach ulcers remain H. pylori and prolonged NSAID use. While high-dose oral B12 supplements might cause temporary stomach upset, it is not a direct cause of ulcer formation. Anyone concerned about ulcer symptoms should seek a medical diagnosis rather than linking the problem to B12 supplementation.

Frequently Asked Questions

No, there is no evidence that high doses of vitamin B12 cause stomach ulcers. However, some individuals may experience mild gastrointestinal upset, such as nausea or diarrhea, from high-dose oral supplements.

A vitamin B12 deficiency, not an excess, is a known cause of painful mouth ulcers, also known as canker sores. Reversing the deficiency can often resolve the issue.

Yes, long-term use of acid-reducing medications, such as proton pump inhibitors (PPIs), can interfere with the absorption of vitamin B12 and potentially lead to a deficiency.

The two most common causes of stomach ulcers are infection with the bacterium Helicobacter pylori (H. pylori) and the frequent, long-term use of nonsteroidal anti-inflammatory drugs (NSAIDs).

If oral B12 supplements cause stomach irritation, try taking them with food, splitting the dose, or discussing alternative forms with your doctor, such as sublingual tablets or injections.

If you experience recurring mouth ulcers alongside symptoms like extreme fatigue, a sore tongue, or neurological problems, a B12 deficiency may be the cause. A blood test can confirm a deficiency.

Yes, H. pylori infection can cause inflammation in the stomach that impairs vitamin B12 absorption, potentially leading to a B12 deficiency over time.