Warfarin and Fatigue: What’s Known, How Common It Is, and When to Seek Care

Fatigue can occur in people taking warfarin, but it appears to be an infrequent side effect and is not among the most common problems associated with this medication. ^[1] Fatigue is listed in official product information alongside other nonspecific symptoms (such as malaise and lethargy), indicating it has been reported but without a high frequency estimate. ^[2] The most well‑recognized risk with warfarin is bleeding, so new or unusual tiredness should be interpreted carefully especially if it occurs with signs of blood loss. ^[3]

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Does warfarin cause fatigue?

Yes, fatigue has been reported in association with warfarin use. ^[1] Official consumer and professional drug information includes “fatigue,” “lethargy,” and “malaise” among infrequent adverse effects. ^[2] These listings suggest fatigue can happen, but they do not assign a precise percentage, which implies it is not commonly reported compared with bleeding‑related issues. ^[4]

Fatigue can also be secondary to other warfarin‑related problems, most notably bleeding that leads to anemia (low red blood cell count), which often presents with weakness, lightheadedness, and tiredness. ^[3] Because fatigue is a nonspecific symptom, it’s helpful to look for accompanying signs that point to bleeding or other causes. ^[5]

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How common is fatigue on warfarin?

Official labeling describes fatigue as “reported infrequently,” without a quantified rate. ^[1] Consumer medication guides similarly list fatigue among possible adverse effects but emphasize bleeding as the primary risk to monitor. ^[2] Clinical literature consistently identifies bleeding as the predominant adverse effect of warfarin, and does not highlight fatigue as a frequent dose‑limiting problem. ^[6] Overall, fatigue seems to be uncommon or variable, and when present, it may reflect another issue (like bleeding or anemia) rather than a direct drug effect. ^{[3] [7]}

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When to seek medical advice

You should contact a healthcare provider promptly if fatigue is new, worsening, or accompanied by any signs of bleeding. ^[3]

• Pain, swelling, or general discomfort. ^[3]
• Headaches, dizziness, or weakness. ^[3]
• Unusual bruising or bruises that appear or enlarge without a clear cause. ^[3]
• Nosebleeds or bleeding gums. ^[3]
• Cuts that take a long time to stop bleeding. ^[3]
• Heavier‑than‑normal menstrual or vaginal bleeding. ^[3]
• Pink or brown urine. ^[3]
• Red or black (tarry) stools. ^[3]
• Coughing up blood. ^[3]
• Vomiting blood or material that looks like coffee grounds. ^[3]

These are standard warning signs for warfarin‑associated bleeding, and experiencing fatigue alongside any of them should prompt evaluation. ^[5] Because the risk of hemorrhage increases markedly when anticoagulation is above the therapeutic range, urgent assessment is important if you have symptoms suggestive of blood loss. ^[7]

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Practical steps if you feel fatigued

• Do not stop warfarin on your own; call your clinician for guidance and consider an INR check to ensure your level is in range. ^[6]
• Keep track of any bleeding signs, bruising, or color changes in urine or stool and report them. ^[3]
• Review other possible contributors (sleep, diet, new medications or supplements) with your care team, as warfarin has many interactions. ^[6]
• Ask whether a blood count is needed to rule out anemia if fatigue persists. ^[3]

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Key points to remember

• Fatigue is a recognized but infrequent side effect of warfarin. ^[1]
• Bleeding is the primary safety concern, and fatigue can be a clue to anemia from bleeding. ^[3]
• Seek medical advice promptly if fatigue is accompanied by any bleeding signs listed above. ^{[5] [3]}
• Regular monitoring (including INR) helps keep warfarin safe and effective. ^[6]

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Summary Table: Fatigue vs. Bleeding Red Flags on Warfarin

Item	What It Means	What To Do
Fatigue alone	Infrequent side effect; can be nonspecific	Discuss with your clinician, review INR and potential interactions; consider basic labs if persistent. [1] [2] [6]
Fatigue + dizziness/weakness	Could indicate anemia or bleeding	Seek prompt medical advice; check for other bleeding signs; consider urgent INR and blood count. [3] [5] [7]
Fatigue + bruising/nosebleeds/gum bleeding	Suggestive of bleeding risk	Contact your provider right away; do not stop warfarin without guidance. [3] [5]
Fatigue + red/black stools or pink/brown urine	Strong signs of internal bleeding	Seek immediate care; this can be serious. [3]

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Bottom line

Fatigue can occur with warfarin, but it is generally reported infrequently and is not among the most common side effects. ^[1] Pay close attention to any accompanying bleeding symptoms; if fatigue appears with signs of blood loss, contact your healthcare provider promptly for evaluation and INR testing. ^{[3] [6]}