Is Vitamin B12 (high-dose) Safe with Vitamin B12?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
If taking metformin long-term, have B12 serum levels checked annually. Supplementation may be required. High-dose B12 supplements are generally safe but inform your physician of all supplements being taken.
Why this interaction occurs
Metformin reduces B12 absorption via calcium-dependent ileal membrane antagonism. While B12 supplementation helps correct deficiency, excessively high supplemental doses (>1000mcg) rarely interact with medications but require medical oversight in renal impairment due to accumulation risk.
Evidence
Evidence level: strong.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 889,644 reports mentioning Vitamin B12. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Vitamin B12 + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
All Vitamin B12 (high-dose) interactions → · All Vitamin B12 interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.