Omeprazole and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Omeprazole
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
Warfarin is a blood thinner, and the amount in your blood has to stay in a careful window. Too much and you can bleed too easily, too little and it may not protect you from clots. Omeprazole, a common stomach acid medicine, can nudge that balance in either direction. Studies show it may change how much warfarin your body keeps around, and it can shift your INR (the blood test that tracks your warfarin level).
The good news is this is very manageable. Your care team can check your INR and fine-tune your warfarin dose so you stay right where you should be. Please don't start or stop either medicine on your own, just talk with your pharmacist or doctor.
Effect: Altered warfarin exposure and INR with concomitant omeprazole. Neither drug is a prodrug, so effect follows the parent-drug PK.
- Mechanism: Mixed. Omeprazole can inhibit CYP2C19-mediated metabolism of warfarin (raising exposure/INR) while also inducing CYP1A2 (potentially lowering exposure/INR). Net direction varies by patient.
- Magnitude: In 21 healthy subjects, omeprazole 20 mg/day produced a mean ~11% decrease in Thrombotest; case reports describe INR/PT elevations.
- Onset: Delayed. Evidence: Probable. Severity: Major (warfarin is narrow therapeutic index).
- Management: Monitor INR/PT closely and adjust warfarin dose to target range, especially when starting, stopping, or changing the omeprazole dose.
What happens
Altered warfarin exposure and altered INR
Interaction Deep Dive
When omeprazole (an inducer of CYP1A2) is given together with warfarin (a CYP1A2 substrate), warfarin exposure may fall and INR may decline as well. The CYP1A2 induction potential should be taken into account when concomitant medications are initiated, discontinued, or have their dose modified2. Following the combined use of omeprazole and warfarin, prothrombin time and INR values may rise41. Such increases in prothrombin time and INR can result in abnormal bleeding and even death. INR and prothrombin time should be monitored, with the warfarin dose adjusted as necessary to keep the INR within the target range1. A controlled study involving 21 healthy subjects found that concurrent administration of omeprazole (20 mg daily) with warfarin produced a mean reduction in the Thrombotest of approximately 11%3.
Why it happens (mechanism)
Reduced warfarin metabolism; induction of CYP1A2-mediated metabolism of warfarin
How to manage this interaction
These two are often used together safely, but because warfarin has such a narrow safety window, your care team keeps a close eye on things.
- Keep taking both exactly as prescribed unless your prescriber tells you otherwise.
- Expect more frequent INR checks, especially in the first weeks after starting or stopping omeprazole or changing its dose.
- Your warfarin dose may be adjusted and individualized by your team to keep your INR in target range.
- Report signs of too much thinning (unusual bruising, bleeding gums, blood in urine or stool, dark stools) or of clotting right away.
Bring up any new medicines, including over-the-counter ones, with your pharmacist.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In 21 healthy volunteers, giving oral omeprazole 20 mg daily together with oral warfarin (average dose, 4.7 mg daily) produced slight rises in plasma (R)-warfarin concentrations (12%), while having no effect on plasma levels of (S)-warfarin 3.
Common questions
Can I take Omeprazole and Warfarin together?
Omeprazole can shift your warfarin level and INR, so your care team will check your INR more often and adjust your warfarin dose to keep you in range. Keep taking both as prescribed and report any unusual bleeding or bruising. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Omeprazole and Warfarin interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
How is the Omeprazole and Warfarin interaction managed?
These two are often used together safely, but because warfarin has such a narrow safety window, your care team keeps a close eye on things. Keep taking both exactly as prescribed unless your prescriber tells you otherwise. Expect more frequent INR checks, especially in the first weeks after starting or stopping omeprazole or changing its dose. Your warfarin dose may be adjusted and individualized… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Omeprazole or Warfarin need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (4)
- Product Information: KONVOMEP(TM) powder for oral suspension, omeprazole sodium bicarbonate powder for oral suspension. Azurity Pharmaceuticals Inc (per manufacturer), Woburn, MA, 2022. DailyMed
- Product Information: WARFARIN SODIUM oral tablets, warfarin sodium oral tablets. Teva Pharmaceuticals (per Dailymed), Parsippany, NJ, 2023. DailyMed
- Sutfin T, Balmer K, Bostrom H, et al: Stereoselective interaction of omeprazole with warfarin in healthy men. Ther Drug Monit 1989; 11:176-184. PubMed
- Product Information: Coumadin (R) Tablets and Injection, Warfarin sodium tablets and injection. Bristol-Myers Squibb Company, Princeton, NJ, 2005. DailyMed
Keep reading about Warfarin
Keep reading about Omeprazole
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