NutriStack
Cimetidine and Vitamin B12, a caution.
Cimetidine reduces gastric acid and pepsin secretion enough to impair the release of dietary B12 from food protein. The Kaiser study linked two or more years of any H2 blocker use to a 25% higher risk of B12 deficiency, and cimetidine has the strongest acid-suppression profile of the H2 class. Risk rises in elderly patients, vegetarians, and those on chronic acid suppression.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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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
- Cimetidine and Vitamin B12
- Pair type
- Caution
- Evidence (highest tier)
- Moderate
- Source citations
- 2 sources
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Moderate evidence
Caution
What is happening. Cimetidine reduces gastric acid and pepsin secretion enough to impair the release of dietary B12 from food protein. The Kaiser study linked two or more years of any H2 blocker use to a 25% higher risk of B12 deficiency, and cimetidine has the strongest acid-suppression profile of the H2 class. Risk rises in elderly patients, vegetarians, and those on chronic acid suppression.
Mechanism. Cimetidine reversibly blocks parietal cell H2 receptors, lowering gastric acid and pepsin. Both are needed to cleave cobalamin from dietary protein before intrinsic factor can bind it for ileal absorption.
Recommendation. If you take cimetidine daily for more than a year or two, ask for a serum B12 (with methylmalonic acid if borderline) check periodically. A daily methylcobalamin supplement is sensible and does not require gastric acid for absorption.
Sources (2)
- Lam JR, Schneider JL, Zhao W, Corley DA. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-42. PMID 24327038
- Miller JW. Proton Pump Inhibitors, H2-Receptor Antagonists, Metformin, and Vitamin B-12 Deficiency: Clinical Implications. Adv Nutr. 2018;9(4):511S-518S. PMID 30032223
Stack Score
How this pair moves the number.
Effect on the composite score
If both Cimetidine and Vitamin B12 are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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