Oxandrolone and Warfarin: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 9, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Warfarin
Oxandrolone
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
Increased warfarin exposure, increased INR, increased anticoagulant response and increased risk of bleeding
Interaction Deep Dive
Coadministration of warfarin (CYP2C9 substrate) and oxandrolone (CYP2C9 inhibitors) may increase warfarin exposure and may increase INR. Consider the CYP2C9 inhibition potential when starting, stopping, or changing dose of concomitant medications. Closely monitor INR if a concomitant CYP2C9 inhibitor is used with warfarin6. Anabolic steroids may increase the anticoagulant response to oral anticoagulants, such as anisindione. In a multi-dose study of healthy subjects (n=15), concurrent treatment with warfarin and oxandrolone produced clinically significant increase in the mean half-life and AUC of the isomeric metabolites of warfarin; this required substantial reductions in warfarin dose in order to maintain a therapeutic target level (1.5) in INR values 8. A number of case reports have demonstrated that coadministration of oral anticoagulants and 17-alkylated androgens (oxandrolone, fluoxymesterone) has resulted in a prolonged prothrombin time and hemorrhages 24.
Why it happens (mechanism)
Inhibition of CYP2C9-mediated metabolism of warfarin
Literature reports
3 reports — tap to read
a) Anabolic steroids have been well documented to cause important interactions with dicumarol. The anabolic steroids enhance dicumarol's anticoagulant activity perhaps through reductions in clotting factor formation and increased clotting factor degradation. The 17-alpha-alkylated steroids (oxandrolone, fluoxymesterone, oxymetholone, methylTESTOSTERone, methandrostenolone, stanozolol) appear to be more likely to induce this reaction than the non-substituted steroids 12345.
b) A mean increase in R-warfarin half-life occurred in patients receiving warfarin and oxandrolone concomitantly. In a multidose study, 16 healthy patients were administered oxandrolone 5 or 10 mg twice daily while also receiving warfarin. A mean increase in R-warfarin half-life from 35.2 to 79.2 hours occurred as did a mean increase in the S-warfarin half life. A 5.5 fold decrease in mean warfarin dose from 6.13 mg daily to 1.13 mg daily was necessary to maintain a target INR of 1.5. INR must be closely monitored for up to 4 weeks or until a stable INR has been achieved. Once oxandrolone therapy has been completed a retitration of the warfarin dose is necessary 7.
c) Concurrent treatment with warfarin and oxandrolone produced clinically significant increases in the mean half-life and area under the concentration-time curve (AUC) of the isomeric metabolites of warfarin. In a multidose study, healthy subjects (n=15) received concomitant treatment with oxandrolone 5 or 10 milligrams (mg) twice daily and warfarin (mean daily dose of 6.13 mg). For S-warfarin, the mean half-life increased from 26 to 48 hours and AUC increased from 4.55 nanograms x hour/milliliter (ng x hr/mL) to 12.08 ng x hr/mL); similar increases were observed for the R-warfarin isomer (actual values not available). Microscopic hematuria was confirmed in 9 patients, and 1 patient exhibited gingival bleeding. A 5.5-fold decrease in mean daily warfarin dose was required (from 6.13 mg/day to 1.13 mg/day) in order to maintain a target International Normalization Ratio of 1.5 8.
Common questions
Can I take Oxandrolone and Warfarin together?
Increased warfarin exposure, increased INR, increased anticoagulant response and increased risk of bleeding Always confirm with your pharmacist or prescriber before making any change.
How serious is the Oxandrolone 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 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 Oxandrolone 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 (8)
- Schrogie JJ & Solomon HM: The anticoagulant response to bishydroxycoumarin. II. The effect of D-thyroxine, clofibrate, and norethandrolone. Clin Pharmacol Ther 1967; 8:70-77. PubMed
- Lorentz SM & Weibert RT: Potentiation of warfarin anticoagulation by topical testosterone ointment. Clin Pharm 1985; 4:332-334.
- Robinson BH, Hawkins JB, Ellis JE, et al: Decreased anticoagulant tolerance with oxymetholone. Lancet 1971; 1:1356. PubMed
- Longridge RG, Gillam PM, & Barton GM: Decreased anticoagulant tolerance with oxymetholone. Lancet 1971; 2:90. PubMed
- Edwards MS & Curtis JR: Decreased anticoagulant tolerance with oxymetholone. Lancet 1971; 2:221. PubMed
- Product Information: WARFARIN SODIUM oral tablets, warfarin sodium oral tablets. Teva Pharmaceuticals (per Dailymed), Parsippany, NJ, 2023. DailyMed
- Personal Communication: Herbert Henney III, Pharm.D. Medical Affairs. Bio-Technology General Corp. April 19, 2002.
- Product Information: OXANDRIN(R) tablets, oxandrolone tablets. Savient Pharmaceuticals, Inc. East Brunswick, NJ, 2005. DailyMed
Keep reading about Warfarin
Keep reading about Oxandrolone
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