Supplement · Grade A

Vitamin B12 and medications.

Every documented pair, every citation. Below: 3 documented pairs grouped by mechanism.

Vitamin B12 is in the Distil supplement database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.

Below are the 3 documented pairs we have explicitly assessed for Vitamin B12: 3 amber. The pairs cluster around 1 mechanism: Absorption interference. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not listed here is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by medication, and the missing-item form at the bottom of the page routes any uncatalogued medication into our next curation pass.

Documented interactions

Absorption interference

Amber Lansoprazole

Long-term lansoprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. If you take lansoprazole long term, ask your GP about an annual B12 blood test.

PMID 24327038 · BNF: Lansoprazole

Amber Metformin

Long-term metformin reduces vitamin B12 absorption in 10 to 30 percent of patients. After a year or more of daily use, ask your GP about an annual B12 blood test. Supplemental B12 (1000 mcg cyanocobalamin daily, or higher doses less frequently) reverses the deficiency in most people.

PMID 20488910 · PMID 26900641

Amber Omeprazole

Long-term omeprazole use reduces stomach acid and slows how well your body absorbs vitamin B12 from food. After about two years of daily use, B12 deficiency becomes notably more likely. If you take omeprazole long term, ask your GP about an annual B12 blood test.

PMID 24327038 · BNF: Omeprazole

What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope. Use the checker below to surface any medication, and submit a missing item if you take something we have not catalogued.

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For adults over 18. This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.

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How we decide

How we grade severity, choose what's in scope, and what we exclude.

Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.

Read the full methodology

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Distil's interactions database is reviewed and updated every quarter. We grade evidence transparently and publish our methodology, including every database change, at /about/methodology. This tool is information, not a substitute for clinical judgement. If you take medication and supplements together, your GP or pharmacist can review your full regimen against your medical history. If you want a comprehensive personalised stack reasoned against this same database, the Distil report is the next step up.