Based on NIH | Is frequent urination a side effect of warfarin?

Short answer

Frequent urination is not a typical side effect of warfarin. The most well‑recognized urinary issues with warfarin are signs of bleeding in the urinary tract, such as pink, brown, or red urine (hematuria), rather than increased urinary frequency. ^{[1] [2]} Warfarin can also, in rare circumstances, contribute to kidney problems related to bleeding within the kidney, which may show up as blood in the urine and changes in kidney function, not as the urge to urinate more often. ^{[3] [4]}

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What warfarin commonly affects

• Bleeding risks: Warfarin’s primary adverse effect is bleeding, and guidance for patients emphasizes watching for urine that is pink, brown, or red, and for black or red stools. These are warning signs of bleeding. ^{[1] [2]}
• Urinary tract bleeding indicators: “Blood in your urine” is specifically listed among the signs to call your healthcare provider about. This reflects hematuria, not urinary frequency. ^{[5] [1]}

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Rare kidney‑related effects

• Warfarin‑related nephropathy: In settings of high anticoagulation (often with INR above the therapeutic range), bleeding through the kidney’s filters (glomeruli) can occur, leading to hematuria and possible acute kidney injury. This condition presents with blood in the urine and kidney function changes, rather than increased urination. ^{[4] [6]}
• Monitoring in kidney disease: People with pre‑existing kidney problems may need closer monitoring, because bleeding risks including blood in urine can be higher. This heightened monitoring is aimed at detecting bleeding and kidney injury, not urinary frequency. ^{[5] [3]}

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If you are urinating frequently

Frequent urination has many potential causes unrelated to warfarin, such as urinary tract infections, overactive bladder, high fluid or caffeine intake, diuretics (“water pills”), diabetes, prostate enlargement (in men), or pregnancy. Because warfarin can increase bleeding risk, any new urinary symptom should still be assessed especially if there is discoloration of urine, pain, fever, or weakness. If you notice pink, brown, or red urine, or clots, contact a clinician promptly. ^{[1] [2]}

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When to seek medical care

• Urgent signs: Pink/brown/red urine, black/red stools, heavy menstrual bleeding, nose or gum bleeding that won’t stop, coughing or vomiting blood, new severe headaches, dizziness, weakness. These warrant prompt medical attention while on warfarin. ^{[1] [2]}
• Kidney concern: If your INR has been supratherapeutic (above target) and you develop hematuria, let your clinician know; they may check kidney function and adjust therapy. This helps prevent warfarin‑related kidney complications. ^{[4] [3]}

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Bottom line

• Frequent urination itself is not recognized as a warfarin side effect. The key urinary adverse effect to watch for is blood‑tinged or discolored urine indicating bleeding. ^{[1] [2]}
• If frequent urination occurs, consider other common causes, but remain vigilant for any bleeding signs while taking warfarin and seek care if they appear. ^{[1] [2]}