What medication stops B12 absorption? A comprehensive guide

October 9, 2025 •

3 min read

The long-term use of certain medications significantly increases the risk of developing a vitamin B12 deficiency, with one large study finding a 65% higher risk among chronic proton pump inhibitor users. For patients and healthcare providers, understanding what medication stops B12 absorption is crucial for proper management and prevention.

Quick Summary

Numerous medications, including metformin, proton pump inhibitors, and H2 blockers, interfere with vitamin B12 absorption through varied mechanisms. These drug-nutrient interactions increase deficiency risk, particularly with higher doses or longer duration. This necessitates patient monitoring and potential supplementation. Recreational nitrous oxide also causes irreversible B12 inactivation.

Key Points

Metformin is a common culprit: Long-term use of the diabetes medication metformin can significantly interfere with B12 absorption by disrupting absorption in the small intestine.
Acid reducers are a major factor: Proton Pump Inhibitors (PPIs) and H2 blockers inhibit the stomach acid needed to release vitamin B12 from food, increasing deficiency risk with chronic use.
Nitrous oxide causes irreversible damage: Recreational use of nitrous oxide (laughing gas) is particularly dangerous because it directly inactivates vitamin B12, which can lead to rapid and severe neurological problems.
Other medications can also interfere: Drugs for gout (colchicine), certain antibiotics, and antiseizure medications can also contribute to B12 malabsorption.
Monitoring is key for long-term users: Regular monitoring of B12 levels is recommended for individuals taking high-risk medications over long periods, especially those with other risk factors.
Supplementation can help: Treatment for medication-induced deficiency often involves B12 supplementation, either orally or via injection, depending on the severity of the malabsorption.

Understanding the Complex Path of B12 Absorption

Vitamin B12 is essential for nerve function, red blood cell formation, and DNA synthesis. Its absorption is a complex process starting in the stomach where acid releases B12 from food proteins. It then binds to intrinsic factor in the small intestine for absorption in the ileum. Medications that disrupt stomach acid, pancreatic function, or the ileum can hinder this process, leading to deficiency.

Key Medications That Inhibit B12 Absorption

Several medications interfere with B12 absorption, with risk often increasing with dosage and duration.

Metformin

Metformin, used for diabetes, is a common cause of B12 malabsorption. The risk correlates with dose and duration, potentially involving altered intestinal function and reduced ileal uptake.

Gastric Acid Inhibitors (PPIs and H2 Blockers)

PPIs (like omeprazole) and H2RAs (like famotidine) reduce stomach acid, essential for releasing food-bound B12. Long-term use, especially in older adults, increases deficiency risk.

Nitrous Oxide

Nitrous oxide, used recreationally and in medicine, rapidly and irreversibly inactivates B12, causing severe neurological damage, even after a single exposure.

Colchicine

This gout medication can interfere with B12 absorption by affecting the ileal mucosa.

Other Notable Medications

A variety of other medications can also impact B12 levels or absorption:

Aminosalicylic acid
Certain antibiotics (e.g., chloramphenicol, neomycin)
Antiseizure medications (e.g., phenobarbital, phenytoin)
Bile acid sequestrants (e.g., cholestyramine)
Chronic excessive alcohol use

Comparison of Common B12-Blocking Medications


Medication Class	Example(s)	Primary Mechanism of Action	Typical Onset of Deficiency	Risk Factors
Metformin	Metformin	Interferes with ileal absorption by affecting calcium availability, altering motility.	Long-term use (months to years), increasing with dose.	High dose, long duration, diabetes, pre-existing risk.
Gastric Acid Inhibitors (PPIs & H2RAs)	Omeprazole, Famotidine	Reduces stomach acid, preventing B12 cleavage from food proteins.	Chronic use (2+ years).	Long duration, older age, high dose.
Nitrous Oxide	Recreational use (whippets), anesthesia	Irreversibly inactivates active vitamin B12.	Can be rapid, with potential for single-exposure harm.	Recreational abuse, underlying deficiency.
Colchicine	Colchicine	Alters the function of the ileal mucosa.	Dose-dependent, can occur relatively quickly.	Long-term use, higher doses for gout treatment.
Antiseizure Drugs	Phenobarbital, Phenytoin	Mechanism not fully understood, but can reduce absorption.	Variable; chronic use increases risk.	Chronic use, multiple medications.

Managing Medication-Induced B12 Deficiency

Regular monitoring of B12 levels may be recommended for long-term users of medications like metformin or PPIs. If a deficiency is detected, treatment options include supplementation via high-dose oral tablets or injections for severe cases. Dietary adjustments can help, and medication review may be necessary, but never stop medication without consulting a healthcare professional. Complete cessation of recreational nitrous oxide is crucial. Early treatment is most effective.

Conclusion

Understanding which medications interfere with B12 absorption is vital for long-term health management. Metformin and gastric acid inhibitors are common culprits, alongside others including recreational nitrous oxide. Due to the potential for serious neurological issues, vigilance for deficiency symptoms and open communication with healthcare providers are essential. Monitoring and supplementation can effectively manage these risks. For more information, the National Institutes of Health (NIH) Office of Dietary Supplements fact sheet on Vitamin B12 is a valuable resource. Always consult a healthcare professional for specific medical advice.

Frequently Asked Questions

Yes, long-term use of metformin is a known cause of vitamin B12 deficiency. The risk increases with higher doses and longer treatment duration, and periodic monitoring is recommended for at-risk patients.

Yes, Proton Pump Inhibitors (PPIs) like omeprazole and Histamine H2 Receptor Antagonists (H2RAs) like famotidine reduce stomach acid. This acid is necessary to release B12 from food, so chronic use can lead to malabsorption, particularly of food-bound B12.

Nitrous oxide irreversibly oxidizes and inactivates vitamin B12, leading to a rapid functional deficiency. This can cause severe neurological damage and other complications, especially with recreational abuse.

Oral B12 supplements are generally not affected by PPIs and H2 blockers because the vitamin is in an unbound, crystalline form that does not require stomach acid for absorption. However, this does not apply to B12 from food sources.

Several antibiotics can interfere with B12, including chloramphenicol, gentamicin, neomycin, and tobramycin. These drugs can disrupt B12 utilization or absorption through different mechanisms.

No, you should never stop or change a prescribed medication without first consulting your doctor. They can determine if a deficiency exists and recommend appropriate management, such as supplementation or an adjusted dosage.

Symptoms can include fatigue, pale skin, sore tongue (glossitis), neurological problems like numbness or tingling (neuropathy), balance issues, and cognitive changes.