Omeprazole

Limits on what this shows

• Key negative or null findings: Other omeprazole studies located in the same literature search ran in the opposite direction: Nasrullah Q, et al. Pharmaceuticals 2022 (correction 2024) reported omeprazole prevented colistin-induced nephrotoxicity in rats, and Gao X, et al. Chem Biol Interact 2019 reported omeprazole protected against cisplatin-induced nephrotoxicity; both are animal/in vitro studies and were not independently retrieved in full text for this dossier beyond their titles and journals, so no statistics from them are cited here, but their direction (protective, not injurious) is itself relevant counter-evidence to a uniform "mitochondrial burden" narrative.
• At-risk subgroups: None can be specified from evidence confined to a cell-free assay and a cultured cell line.
• Dose/duration: Not established in vivo; the Tonazzi assay used a defined in vitro omeprazole concentration in a reconstituted membrane system, which does not translate directly to a human dose or duration of exposure.

Regulatory status

Not addressed in the Prilosec label; the label was checked specifically for mitochondrial, oxidative-stress, or ATP-related language during this expansion and none was found.

Population evidence

None at Tier A. Tier B only: Tonazzi A, Eberini I, Indiveri C. "Molecular mechanism of inhibition of the mitochondrial carnitine/acylcarnitine transporter by omeprazole." PLOS ONE 2013 (PMID 24349247): in a cell-free reconstituted-proteoliposome assay, externally added omeprazole inhibited the mitochondrial carnitine/acylcarnitine antiporter, an effect that was partially reversible. Fontecha-Barriuso M, et al. "Molecular pathways driving omeprazole nephrotoxicity." Redox Biology 2020 (PMID 32092686): in cultured human renal tubular cells, omeprazole exposure triggered weak caspase-3 activation and cell-death signaling under investigation in a nephrotoxicity-screening context.

Mechanism

Named but indirect and confined to isolated systems. Carnitine/acylcarnitine transporter inhibition, if replicated in intact cells at achievable drug concentrations, could impair mitochondrial import of long-chain fatty acids for beta-oxidation; the renal cell-death finding is a separate toxicology-screening result (high-concentration exposure of a cultured cell line) and was not shown to generalize to any other tissue or to physiological omeprazole dosing.

Counter-evidence held on record

The literature identified for omeprazole and mitochondrial endpoints is directionally inconsistent: isolated-system inhibition findings sit alongside multiple animal studies showing omeprazole protecting mitochondria-rich tissue (kidney, lung) from injury by other agents. No study reviewed measured mitochondrial function, membrane potential, or respiration directly in omeprazole-treated intact animals or humans. This is isolated in vitro mechanistic evidence only and should not be presented as omeprazole causing mitochondrial harm in patients. It is not grounds for CoQ10, carnitine, or any other "mitochondrial support" supplementation.

Limits on what this shows

• Key negative or null findings: Calleja LF, et al. FEBS Journal 2021: in an Escherichia coli model overexpressing ALDH1A1, omeprazole activation of that enzyme protected cells from oxidative stress, the opposite direction from a burden claim. Yang, et al. Journal of Maternal-Fetal and Neonatal Medicine 2023: in peripheral blood mononuclear cells from premature infants, omeprazole activated the aryl hydrocarbon receptor and reduced hyperoxia-induced oxidative stress, again the opposite direction, in a different model and population than Dries et al.
• At-risk subgroups: Cannot be specified given that the positive human signal was not verifiable in quantitative detail.
• Dose/duration: Dries et al. is described as studying use beyond six months; no further dose or duration detail was retrievable.

Regulatory status

Not addressed in the Prilosec label.

Population evidence

Dries LS, et al. "Cognition, oxidative stress and vitamin B12 levels evaluation on patients under long-term omeprazole use." Journal of Pharmacy and Pharmacology, 2022;74(4):547-555 (PMID 33793790, verification limited, see Sources). A PubMed listing for this human study of patients using omeprazole longer than six months describes its objective as evaluating cognitive performance, oxidative stress, and B12 levels, and its conclusion as suggesting long-term omeprazole use may induce an oxidative stress response. The specific biomarkers measured, sample size, comparator group, and effect sizes could not be retrieved in full text through the sources accessible for this review, so no statistic from this study is cited here.

Mechanism

Not clearly named in the material retrievable for this dossier. A plausible but unconfirmed route would run through achlorhydria-associated dysbiosis (see the new Gut microbiome risk entry above) or through B12/micronutrient shifts, but no source reviewed traced oxidative stress markers to a specific omeprazole-driven pathway.

Counter-evidence held on record

The direction of effect is inconsistent across the identified literature: one human study's conclusion points toward increased oxidative stress, while two mechanistic studies in different cell models found omeprazole reduced oxidative stress. The positive human finding could not be verified beyond its title, journal citation, and stated conclusion, and per this dossier's citation-integrity standard, no numeric result from it is reported above. This is a low-confidence, directionally contested signal, not an established finding. It is not grounds for antioxidant supplementation, and the protective findings in other models should not be read as a reason to use omeprazole for that purpose either, since none of this literature tested supplementation or off-label use.

Limits on what this shows

• Key negative or null findings: The Hutchinson cohort was selected for hereditary hemochromatosis, a condition of iron overload in which reduced absorption is the therapeutic goal rather than a harm, which limits how directly this evidence generalizes to a healthy or iron-deficient omeprazole user. A separately named clinical report describing suboptimal ferrous sulfate response in iron-deficient patients taking omeprazole could not be verified in full text for this dossier and is not used to support this grade.
• At-risk subgroups: Patients being treated for iron-deficiency anemia while on long-term omeprazole, and anyone relying mainly on nonheme, plant-based dietary iron sources.

Regulatory status

Not addressed in the current Prilosec label.

Population evidence

Hutchinson et al., Gut 2007, studied patients with hereditary hemochromatosis given either omeprazole 20 mg or lansoprazole 30 mg daily. A 7-day course of PPI therapy significantly reduced measured postprandial nonheme iron absorption in 14 patients (area under the serum iron curve, 2145 vs. 1059; peak fractional absorption, 20.5% vs. 11.0%; maximum serum iron, 13.6 vs. 6.1 micromol/L; p<0.001 to p<0.01), and annual phlebotomy volume needed to maintain target iron stores fell in 7 paired patients on chronic PPI therapy (from 2.5 to 0.5 L/year, p<0.001). Because both PPIs were used without results broken out by individual drug, and this population was specifically trying to reduce iron stores, this is supportive but not an omeprazole-isolated, general-population finding.

Mechanism

Named. Dietary nonheme iron is predominantly ferric (Fe3+) and must be reduced to ferrous (Fe2+) iron, a step assisted by gastric acid, before enterocyte uptake; suppressing acid secretion impairs this reduction.

Counter-evidence held on record

The best-verified human data for this mechanism comes from a small, iron-overload population where reduced absorption is the intended effect, not a harm; it does not by itself establish that a healthy or iron-deficient patient on long-term omeprazole will develop iron deficiency. No randomized trial comparing oral iron repletion success with and without omeprazole was verified in full text for this dossier. This is a mechanistic and small-study signal, not an established population-level deficiency risk. A poor response to oral iron therapy in a patient on long-term omeprazole is worth raising with a prescriber, but omeprazole use alone is not grounds for iron supplementation.

Limits on what this shows

• Key negative or null findings: See the existing Iron entry above for the Hutchinson-specific limitations. For this expansion, the added limitation is that Chen et al. 2025 could not be verified in quantitative detail, so it neither strengthens nor weakens the existing grade; it is recorded as a source to revisit if full text becomes accessible.
• At-risk subgroups: Unchanged from the existing Iron entry above.
• Dose/duration: Unchanged from the existing Iron entry above; Chen et al. did not add a new duration threshold that could be verified.

Regulatory status

Unchanged from the existing Iron entry above: not addressed in the current Prilosec label.

Population evidence

The existing Iron entry above rests on Hutchinson et al., Gut 2007, a hereditary hemochromatosis cohort. Searching specifically for a general-population (non-hemochromatosis) signal for this expansion surfaced Chen TP, et al., "Bone health, renal outcomes, and iron deficiency anaemia in proton pump inhibitor versus histamine-2 receptor antagonist users: a retrospective cohort study," BMJ Open Gastroenterology 2025, a retrospective cohort using the TriNetX global collaborative network comparing PPI and H2RA users for, among other outcomes, iron deficiency anemia. This is a genuinely different population from Hutchinson (general PPI users rather than a hemochromatosis cohort), but its abstract, as retrieved for this dossier, states the objective and data source without reporting the quantitative iron deficiency anemia result (hazard ratio, odds ratio, or confidence interval), and does not confirm whether omeprazole is analyzed individually or pooled with other PPIs. No statistic from this source is used to support a grade change.

Mechanism

Unchanged from the existing Iron entry above: gastric acid assists reduction of dietary ferric to ferrous iron before enterocyte uptake.

Counter-evidence held on record

This entry exists to document that the physiological-expansion research pass deliberately did not duplicate or re-grade the mechanism already covered above. See the Overlap map below for how iron findings are counted only once across this dossier. This entry should not be read as a second, independent iron-deficiency finding. It carries no framing or supplementation guidance beyond what the existing Iron entry above already states.

Limits on what this shows

• Key negative or null findings: The absence of results is itself the finding here; see Population evidence above. This differs from a null RESULT (a study that measured copper and found no change) in that no study measuring copper status in acid-suppressed patients was located at all.
• At-risk subgroups: Cannot be specified; no population has been studied for this question.
• Dose/duration: Not applicable; no exposure-response relationship exists in the literature to describe.

Regulatory status

Not addressed in the Prilosec label; copper is not named anywhere in the sections reviewed for this dossier.

Population evidence

None found. Three separate PubMed searches conducted for this expansion (achlorhydria/hypochlorhydria plus copper absorption; achlorhydria plus trace element absorption including copper and zinc; gastric acid suppression plus copper status) each returned zero results.

Mechanism

None established. The National Institutes of Health Office of Dietary Supplements Copper Fact Sheet for Health Professionals was checked directly for this dossier and does not mention proton pump inhibitors, omeprazole, or gastric acid suppression as an influence on copper absorption; it discusses dietary copper intake as the primary determinant of absorption. A pH-dependent-solubility mechanism analogous to the calcium carbonate or nonheme iron entries above was considered but not used to support a grade, because no study, drug-specific or class-level, was found testing it for copper.

Counter-evidence held on record

Not applicable in the usual sense; there is no claim being rebutted and no positive finding being contradicted. What is on record is the search history itself: three independent query formulations, each returning zero PubMed results, plus a direct check of the NIH copper fact sheet. An evidence gap is not evidence of safety. This entry means the question has not been studied for omeprazole, not that omeprazole has been shown not to affect copper status. It is not grounds for copper supplementation, which carries its own risks and should never be started without a documented reason and a clinician's involvement.

Limits on what this shows

• Key negative or null findings: A 2025 systematic review and meta-analysis restricted to randomized controlled trials (Floria et al., Gut Microbes) found that PPI use was not associated with a significantly increased risk of Clostridioides difficile infection, in contrast to the pooled observational literature; this dossier could not independently verify this source's full bibliographic detail (volume, pages, PMID/DOI) beyond a search-results listing, and it is cited with that limitation flagged. Because randomized trials of PPIs are not typically powered or designed around CDAD as a primary endpoint, this null finding narrows rather than eliminates the labeled concern, but it is real, Tier A-level contradicting evidence on the specific infection outcome and is the reason this entry is bounded to ORANGE rather than RED.
• At-risk subgroups: Hospitalized patients (named specifically in the label's CDAD language), patients on long-term continuous therapy, and anyone with additional risk factors for enteric infection (recent antibiotic use, immunosuppression, travel).
• Dose/duration: The label's bacterial-overgrowth finding was demonstrated after 14 days of omeprazole dosing in healthy subjects; the Imhann cohort captured mixed acute-to-chronic real-world use without a clean duration threshold. No dose or duration of omeprazole use has been shown to be free of this compositional effect.

Regulatory status

Prilosec label, section 5.3, "Clostridium difficile-Associated Diarrhea": "Published observational studies suggest that PPI therapy like PRILOSEC may be associated with an increased risk of Clostridium difficile-associated diarrhea, especially in hospitalized patients." Section 12.2 (Pharmacodynamics) reports a direct interventional finding: omeprazole administered for 14 days in healthy subjects produced a significant increase in intragastric concentrations of viable bacteria. Section 12.4 (Microbiology) states that decreased gastric acidity from any cause, including PPIs, increases gastric counts of bacteria normally present in the gastrointestinal tract, and that PPI treatment may lead to a slightly increased risk of gastrointestinal infections such as Salmonella and Campylobacter.

Population evidence

Imhann F, Bonder MJ, Vich Vila A, et al. Gut 2016: cross-sectional analysis of three independent Dutch cohorts totaling 1,815 individuals (a general-population cohort, an IBD cohort, and an IBS cohort with matched controls), using 16S rRNA sequencing. PPI use was scored where participants used omeprazole, esomeprazole, pantoprazole, lansoprazole, dexlansoprazole, or rabeprazole, with omeprazole specifically named as a drug taken by general-population users; roughly 12% of the pooled sample were PPI users. PPI use was associated with a significant decrease in Shannon diversity, with roughly 20% of measured bacterial taxa showing significant compositional change and the oral-cavity genus Rothia markedly increased in PPI users. This is a strong, large, drug-named finding, but PPI users are pooled rather than omeprazole being isolated from the other five drugs scored, and the design is cross-sectional.

Mechanism

Named: gastric acid is a chemical barrier that kills most ingested and oropharyngeal bacteria before they reach the small intestine. Suppressing acid secretion removes this barrier, allowing oral and environmental bacteria to colonize the stomach, small intestine, and, on the label's own pharmacology data, to reach higher counts within two weeks of dosing; this is proposed to both reduce protective diversity downstream and to raise the risk of enteric infection by pathogens that would otherwise be acid-killed on ingestion.

Counter-evidence held on record

The Floria et al. 2025 RCT-level meta-analysis found no significant CDAD risk increase, directly contradicting the labeled observational signal for that specific outcome. Imhann is cross-sectional and cannot fully establish that omeprazole caused the observed diversity loss rather than reflecting reverse causation (GERD-related dietary or lifestyle differences) or confounding by indication; the drug's underlying indication (GERD/PUD) is not independently known to alter gut microbiota, but this was not ruled out with a dedicated confounder analysis in the source. This entry documents a real, labeled, mechanistically direct compositional effect, not a settled claim that omeprazole reliably causes C. difficile infection. It is not grounds for probiotic supplementation or any other self-directed gut-health intervention; any concern about recurrent GI infection on long-term omeprazole belongs with a prescriber.

Limits on what this shows

• Key negative or null findings: The cohort is small (98 exposed patients) and single-center; confounding by indication was not fully excluded, since GERD/PUD and the comorbidities that lead to chronic PPI prescribing can independently produce mild anemia of chronic disease. No study reviewed for this dossier directly measured tissue oxygen delivery, oxygen saturation, or erythropoietin response in omeprazole users; "oxygen delivery/utilization" here rests on a hemoglobin/hematocrit proxy, not a direct functional oxygen-transport measurement.
• At-risk subgroups: Patients on chronic (not short-course) PPI therapy, and anyone in whom baseline hemoglobin is already borderline low, where an incremental decline is more likely to become clinically apparent.
• Dose/duration: The cohort was defined as chronic PPI users; the source did not report a minimum duration threshold below which the effect was absent, unlike the label-based magnesium and B12 entries above.

Regulatory status

Not addressed in the current Prilosec label.

Population evidence

Sarzynski E, et al. "Association between proton pump inhibitor use and anemia: a retrospective cohort study." Digestive Diseases and Sciences, 2011 (PMID 21318590). Retrospective cohort in an academic outpatient setting: 98 patients on chronic PPI therapy versus matched controls not on a PPI. Hemoglobin decreased by 0.19 g/dL more in PPI users than controls (P=0.03); the adjusted odds ratio for a hemoglobin decline of 1.0 g/dL or more was 5.03 (95% CI 1.71-14.78, P<0.01), and for a hematocrit decrease of 3% or more was 5.46 (95% CI 1.67-17.85, P<0.01). This dossier could not confirm from the sources retrieved whether omeprazole specifically, versus other PPIs, made up part or all of this cohort, so it is treated as PPI-class evidence rather than an omeprazole-isolated finding.

Mechanism

Not established as independent of the mechanisms already graded above. The most plausible route is that reduced hemoglobin/hematocrit in this cohort reflects the same B12 food-release impairment (graded ORANGE above) and nonheme iron reduction impairment (graded YELLOW above) manifesting as a measurable hematologic outcome, rather than a distinct third pathway. This entry is filed separately because it is a direct functional measurement of oxygen-carrying capacity, which the B12 and iron entries do not themselves provide, not because a new mechanism was identified.

Counter-evidence held on record

This is a single Tier A source, not two independent sources, and by itself cannot support a grade above ORANGE. The hemoglobin/hematocrit decline is plausibly downstream of the already-graded B12 and iron mechanisms rather than an independent physiological pathway, and confounding by indication (the underlying GERD/PUD or comorbid illness that led to PPI prescribing) was not excluded in a retrospective design. This is outcome-level hematologic evidence, not proof of a separate "oxygen delivery" deficiency mechanism distinct from B12 and iron status. It is not grounds for iron or B12 supplementation beyond what those entries already state, and any hemoglobin concern in a long-term omeprazole user should be worked up by a prescriber rather than self-treated.

Limits on what this shows

• Key negative or null findings: Not applicable; no study exists to report a null result from.
• At-risk subgroups: Cannot be specified.
• Dose/duration: Not applicable.

Regulatory status

Not addressed in the Prilosec label. The label does describe omeprazole's own mechanism of action as inhibition of the parietal cell H+/K+ ATPase (sections 12.2/12.3, see the pharmacokinetic basis above); this is the drug's intended therapeutic target, not a nutrient or physiological deficiency finding, and is explicitly not filed here as one (see the Overlap map below).

Population evidence

None found at any tier. The one in vitro finding potentially adjacent to this question, omeprazole's inhibition of the mitochondrial carnitine/acylcarnitine transporter in a cell-free assay (Tonazzi et al. 2013, cited under Mitochondrial burden above), was generated to characterize that transporter, not to measure ATP output, and is filed under Mitochondrial burden rather than double-counted here as direct ATP evidence.

Mechanism

None established for omeprazole and cellular ATP production specifically. A chained hypothesis (omeprazole-associated magnesium loss, graded RED above, impairing magnesium-dependent ATP-synthesizing enzymes) is mechanistically conceivable but was not constructed into a graded finding here, because no source reviewed measured ATP production as a function of omeprazole-associated magnesium status.

Counter-evidence held on record

Not applicable; there is no finding to counter. The search for cellular ATP production evidence surfaced only reviews of PPIs as vacuolar-ATPase-targeting agents in cancer pharmacology, a distinct proton pump from the mitochondrial ATP synthase and not evidence of impaired ATP production in normal human tissue; this was not used to support a grade. An evidence gap is not evidence of safety, and it is also not evidence of harm. This entry should never be rewritten as "omeprazole does not affect energy production"; it means the question has not been directly studied. It is not grounds for any energy-support or mitochondrial supplement.