Does metformin lower vitamin B12?

Updated 3 Nov 2026

Short answer

Yes. A 2016 meta-analysis found B12 levels 57 pmol/L lower after 6 weeks to 3 months of metformin, and 10 of 17 observational studies found lower levels in people who took it.^[1] NICE lists metformin as a risk factor, and says that a deficiency caused by the medicine can be treated with tablets or injections while a person takes it.^[2] In a 2022 review of 7 trials in people on metformin, B12 supplements raised blood B12 in all 5 trials that measured it.^[3]

Sources (3)

Association between metformin and vitamin B(12) deficiency in patients with type 2 diabetes: A systematic review and meta-analysis. Chapman LE, Darling AL, Brown JE Diabetes Metab, 2016. PMID 27130885
Vitamin B12 deficiency in over 16s: diagnosis and management (NG239). National Institute for Health and Care Excellence (NICE), 2024. www.nice.org.uk
The efficacy of vitamin B(12) supplementation for treating vitamin B(12) deficiency and peripheral neuropathy in metformin-treated type 2 diabetes mellitus patients: A systematic review. Pratama S, Lauren BC, Wisnu W Diabetes Metab Syndr, 2022. PMID 36240684

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For education; not medical advice. Talk to a doctor before you start, stop or change a supplement.