NutriStack
Metformin and Methylcobalamin, a synergy.
Metformin reduces serum vitamin B12 by impairing calcium-dependent ileal absorption of B12-intrinsic factor complexes. Meta-analyses report B12 deficiency in roughly 1 in 5 long-term metformin users, with risk rising with dose and duration of therapy and contributing to neuropathy, anemia, and elevated homocysteine. Methylcobalamin (the activated form) supplementation reliably restores B12 status and is often preferred when peripheral neuropathy is a concern.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
Same shape as the other 1,729 pairs in the public database.
From the interaction database
What the row says.
Every entry follows the same shape: what is happening, the mechanism, the recommendation, and the primary literature.
At a glance
- Substances
- Metformin and Methylcobalamin
- Pair type
- Synergy
- Evidence (highest tier)
- Strong
- Source citations
- 2 sources
- Stack Score effect
- +2 to your Stack Score (per scored synergy row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Synergy · Strong evidence
Synergy
What is happening. Metformin reduces serum vitamin B12 by impairing calcium-dependent ileal absorption of B12-intrinsic factor complexes. Meta-analyses report B12 deficiency in roughly 1 in 5 long-term metformin users, with risk rising with dose and duration of therapy and contributing to neuropathy, anemia, and elevated homocysteine. Methylcobalamin (the activated form) supplementation reliably restores B12 status and is often preferred when peripheral neuropathy is a concern.
Mechanism. Metformin disrupts the calcium-dependent uptake of the B12-intrinsic factor complex by ileal cubilin receptors and may alter intestinal motility and B12-binding by bile acids. Methylcobalamin bypasses some of this by providing a directly bioavailable, active form of B12 that is absorbed both via intrinsic factor and passive diffusion at higher doses.
Recommendation. If you take metformin long-term (>1 year), ask for an annual serum B12 check (and methylmalonic acid if B12 is low-normal). If levels are low or you have neuropathy, supplement methylcobalamin (typically 1000 mcg/day orally). Take it with or away from metformin; absorption is not affected by timing.
Sources (2)
- Niafar M, Hai F, Porhomayon J, Nader ND. The role of metformin on vitamin B12 deficiency: a meta-analysis review. Intern Emerg Med. 2015;10(1):93-102. PMID 25502588
- Yang W, Cai X, Wu H, Ji L. Associations between metformin use and vitamin B12 levels, anemia, and neuropathy in patients with diabetes: a meta-analysis. J Diabetes. 2019;11(9):729-743. PMID 30615306
Stack Score
How this pair moves the number.
Effect on the composite score
If both Metformin and Methylcobalamin are in the same stack, this pair applies +2 to your Stack Score (per scored synergy row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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