NutriStack
Omeprazole and Vitamin B12, a caution.
Long-term omeprazole use significantly impairs vitamin B12 absorption. Gastric acid and pepsin are required to release B12 from food proteins before it can bind intrinsic factor. Studies show 65% increased risk of B12 deficiency with >2 years of PPI use.
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
- Omeprazole and Vitamin B12
- Pair type
- Caution
- Evidence (highest tier)
- Strong
- 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 · Strong evidence
Caution
What is happening. Long-term omeprazole use significantly impairs vitamin B12 absorption. Gastric acid and pepsin are required to release B12 from food proteins before it can bind intrinsic factor. Studies show 65% increased risk of B12 deficiency with >2 years of PPI use.
Mechanism. Gastric acid and pepsin are needed to cleave vitamin B12 from dietary proteins. In the achlorhydric environment created by omeprazole, B12 remains protein-bound and cannot transfer to R-protein and subsequently intrinsic factor for absorption in the terminal ileum.
Recommendation. Monitor B12 levels annually during long-term omeprazole therapy. Consider B12 supplementation (sublingual methylcobalamin 1000 mcg/day bypasses the gastric absorption requirement) or periodic B12 injections.
Sources (2)
- Lam JR et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-2442. PMID 24327038
- Choudhury A, Jena A, Jearth V, Dutta AK et al.. Vitamin B12 deficiency and use of proton pump inhibitors: a systematic review and meta-analysis. Expert Review of Gastroenterology & Hepatology. 2023. PMID 37060552
Stack Score
How this pair moves the number.
Effect on the composite score
If both Omeprazole 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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