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Causality: well established
Causality assessment · Causality: well established
Metformin and Vitamin B12 deficiency: is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Metformin ↔ Vitamin B12 deficiency
n=630 co-reports · PRR 10.8 · ROR 10.8
Metformin is a first-line antidiabetic; over years of treatment it reduces ileal absorption of vitamin B12 and can lower serum levels, so vitamin B12 deficiency appears here as 630 co-reports (PRR 10.8). Deficiency develops insidiously and may present as anaemia or peripheral neuropathy, and the label advises periodic B12 monitoring in patients on long-term therapy, particularly with other risk factors.
Regulatory basis: metformin prescribing information — vitamin B12 deficiency with long-term use; periodic monitoring.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Deficiency after months to years |
| Strength | met | PRR 10.8, large |
| Consistency | met | Reproduced across cohorts |
| Specificity | partial | Shared with other biguanides |
| Biological gradient | met | Dose- and duration-related |
| Plausibility | met | Impaired ileal B12 absorption |
| Coherence | met | Fits the mechanism |
| Experiment | met | Trials recorded falls in B12 levels |
| Analogy | met | Analogous to other drug-induced B12 deficiency |
This table is this page's own qualitative read of the literature cited above, not an automated or citation-gated assessment — see the note at the bottom of this page.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for metformin captured vitamin b12 deficiency as a tracked adverse event in a usable structure. Vitamin B12 deficiency develops slowly and is often subclinical, so short-term trials captured falls in B12 levels rather than clinical deficiency as a coded event.