NutriStack
Cimetidine and Iron, a caution.
Cimetidine reduces gastric acid and modestly impairs absorption of oral iron salts, particularly ferrous sulfate. The H2 blocker class is associated with about a 1.6-fold higher risk of iron deficiency on long-term use. Cimetidine also has the strongest acid-suppressing profile of the H2 blockers.
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
- Cimetidine and Iron
- 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 modestly impairs absorption of oral iron salts, particularly ferrous sulfate. The H2 blocker class is associated with about a 1.6-fold higher risk of iron deficiency on long-term use. Cimetidine also has the strongest acid-suppressing profile of the H2 blockers.
Mechanism. Gastric acid converts dietary ferric to absorbable ferrous iron and solubilizes oral iron salts for duodenal uptake by DMT1. Cimetidine blocks H2 receptors on parietal cells, reducing acid output and the resulting absorption.
Recommendation. Take iron supplements at least 2-4 hours apart from cimetidine. Consider iron bisglycinate, which absorbs better at higher gastric pH. Recheck ferritin 3 months after starting iron.
Minimum separation. 120
Sources (2)
- Lam JR, Schneider JL, Quesenberry CP, Corley DA. Proton Pump Inhibitor and Histamine-2 Receptor Antagonist Use and Iron Deficiency. Gastroenterology. 2017;152(4):821-9. PMID 27890768
- Freedberg DE, Kim LS, Yang YX. The Risks and Benefits of Long-term Use of Proton Pump Inhibitors: Expert Review and Best Practice Advice From the American Gastroenterological Association. Gastroenterology. 2017;152(4):706-15. PMID 28257716
Stack Score
How this pair moves the number.
Effect on the composite score
If both Cimetidine and Iron 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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