ModerateBiguanides. Oral antihyperglycemic agents×Water-soluble B-vitamin; cofactor of methionine synthase and methylmalonyl-CoA mutase
Updated · Methodology
Mechanism
The metformin label states it outright: long-term use reduces absorption and serum levels of vitamin B12, and it advises considering this cause in megaloblastic anaemia. The mechanism is calcium-dependent in the terminal ileum, and the effect grows with dose and years of treatment.
Symptoms
Paraesthesia in the feet, unsteady gait, loss of vibration sense. In diabetes the picture is mistaken for diabetic polyneuropathy and treated as such for years while the deficiency continues.
Management
Measure B12 at least yearly in anyone more than four years on metformin, and whenever neuropathy or anaemia appears. A low value does not force metformin withdrawal: supplement B12 orally and keep the antidiabetic. Test as well in patients who also take a proton pump inhibitor, since the two mechanisms add up.
Check the full regimen, not just this pair
Opens the checker with these two drugs prefilled. Add the rest of the regimen and recompute additive risks.
Summary of a multi-drug list →
Medicine list: everything you take in one place →
Sources
- AEMPS: Ficha técnica Metformina Cinfa 850 mg comprimidos EFG (2024)– AEMPS, CIMA, nº registro 68167, sección 4.8
- NIH Office of Dietary Supplements: Vitamin B12 – Health Professional Fact Sheet (2025)– NIH ODS, Vitamin B12, Interactions with Medications