Warfarin and Nevirapine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Nevirapine
Warfarin
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.
What happens
Altered warfarin exposure and an altered INR
Interaction Deep Dive
Concomitant use of nevirapine (CYP3A4 inducer) and warfarin(CYP3A4 substrate) may alter warfarin plasma concentrations3. Coadministration of nevirapine and warfarin may reduce warfarin exposure. It may also reduce INR. Consider the CYP3A4 inhibition potential when starting, stopping, or changing dose of concomitant medications 4. A report described 3 cases of reduced warfarin effectiveness with concomitant administration of nevirapine 6. Also, concomitant use may increase warfarin exposure that may increase the coagulation time. Monitor the INR frequently in patients receiving concurrent nevirapine and warfarin therapy 12 and adjust the warfarin dosage accordingly 3.
Why it happens (mechanism)
Altered warfarin metabolism; induction of CYP3A4-mediated metabolism of warfarin
Literature reports
1 report — tap to read
a) Three cases of reduced warfarin effectiveness with concomitant administration of nevirapine have been reported. A 38-year-old man with primary pulmonary hypertension was administered warfarin 2.5 mg daily while receiving stavudine, lamiVUDine, and nevirapine. His INR quickly dropped from an average 2.1-2.4 to 1.3. An increase of warfarin to 5 mg daily restored anticoagulant activity (INR 2.0). All drugs were discontinued as a result of urticarioid eruption. INR was optimized with a new treatment regimen consisting of warfarin 2.5 mg daily, stavudine, lamiVUDine and saquinavir. A 28-year-old man being treated with zidovudine, lamiVUDine and nevirapine developed proximal deep-vein thrombosis. Warfarin (17 mg a day) was administered. After stopping the nevirapine, warfarin 5 mg daily was sufficient to stabilize the INR within the therapeutic range. Nevirapine was reinstated and warfarin 12 mg daily was required to maintain coagulation within the therapeutic range. Warfarin was administered to a 39-year-old man because of a deep-vein thrombosis in his leg. He was being treated with zidovudine, lamiVUDine, and nevirapine and required warfarin 12.5 mg daily. After nevirapine was discontinued warfarin 7.5 mg a day was sufficient to stabilize the INR within the therapeutic range. Additional studies are needed to investigate the clinical significance of the need for an increased dose of warfarin with concomitantly administered nevirapine 5.
Common questions
Can I take Warfarin and Nevirapine together?
Altered warfarin exposure and an altered INR Always confirm with your pharmacist or prescriber before making any change.
How serious is the Warfarin and Nevirapine 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 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 Warfarin or Nevirapine 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 (6)
- Product Information: VIRAMUNE(R) oral suspension, nevirapine oral suspension. Boehringer Ingelheim Pharmaceuticals Inc (per FDA), Ridgefield, CT, 2024. DailyMed
- Product Information: VIRAMUNE XR(R) oral extended-release tablets, nevirapine oral extended-release tablets. Boehringer Ingelheim Pharmaceuticals Inc (per FDA), Ridgefield, CT, 2024. DailyMed
- U.S. Department of Health and Human Services: Guidelines for the use of antiretroviral agents in HIV-1-Infected adults and adolescents. U.S. Department of Health and Human Services. Washington, DC. 2011.
- Product Information: WARFARIN SODIUM oral tablets, warfarin sodium oral tablets. Teva Pharmaceuticals (per Dailymed), Parsippany, NJ, 2023. DailyMed
- Dionisio D, Mininni S, Barolozzi D, et al: Need for increased dose of warfarin in HIV patients taking nevirapine. AIDS 2001; 15(2):277-278. PubMed
- Dionisio D, Mininni S, Barolozzi D, et al: Need for increased dose of warfarin in HIV patients taking nevirapine (letter). AIDS 2001; 15(2):277-278. PubMed
Keep reading about Nevirapine
Keep reading about Warfarin
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Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
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