Warfarin Side Effects
Medically reviewed by Drugs.com. Last updated on Mar 14, 2025.
Applies to warfarin: oral tablet.
Other dosage forms:
Important warnings
This medicine can cause some serious health issues
Oral route (tablet)
Warfarin can cause major or fatal bleeding.
Regular monitoring of INR should be performed on all treated patients.
Drugs, dietary changes, and other factors affect INR levels achieved with warfarin sodium therapy.
Instruct patients about prevention measures to minimize risk of bleeding and to report signs and symptoms of bleeding.
Serious side effects of warfarin
Along with its needed effects, warfarin may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.
Check with your doctor immediately if any of the following side effects occur while taking warfarin:
Less common side effects
- bleeding gums
- blood in the urine
- bloody stools
- blurred vision
- burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
- chest pain or discomfort
- confusion
- coughing up blood
- difficulty with breathing or swallowing
- dizziness, faintness, or lightheadedness when getting up suddenly from a lying or sitting position
- excessive bruising
- headache
- increased menstrual flow or vaginal bleeding
- nosebleeds
- paralysis
- peeling of the skin
- prolonged bleeding from cuts
- red or black, tarry stools
- red or dark brown urine
- stomach pain with cramping
- sweating
- unexplained swelling
- unusual tiredness or weakness
Rare side effects
- arm, back, or jaw pain
- blue-green to black skin discoloration
- blue or purple toes
- change in consciousness
- chest tightness or heaviness
- chills
- clay-colored stools
- diarrhea
- dizziness
- fainting or loss of consciousness
- fast or irregular breathing
- fast or irregular heartbeat
- fever
- itching or skin rash
- light-colored stools
- loss of appetite
- nausea and vomiting
- pain in the toes
- pain, redness, or sloughing of the skin
- pale skin
- purplish red, net-like, blotchy spots on the skin
- skin blisters
- small red or purple spots on the skin
- stomach pain
- swelling of the eyes or eyelids
- troubled breathing with exertion
- unpleasant breath odor
- unusual bleeding or bruising
- upper right stomach pain
- vomiting of blood
- yellow eyes and skin
Other side effects of warfarin
Some side effects of warfarin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.
Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:
Less common side effects
Rare side effects
- bloated
- change in taste, or bad, unusual, or unpleasant (after) taste
- cold intolerance
- excess air or gas in the stomach or intestines
- full feeling
- general feeling of discomfort or illness
- hair loss or thinning of the hair
- hives or welts
- lack or loss of strength
- pain
- passing gas
- red, sore, or itching skin
- sores, welting, or blisters
- unusual drowsiness, dullness, or feeling of sluggishness
Precautions
It is very important that your doctor check your progress at regular visits to make sure this medicine is working properly. Blood tests, such as an INR, are needed to check for proper dosage and unwanted side effects. Be sure to keep all appointments.
Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant during treatment and for at least 1 month after the last dose. If you think you have become pregnant while using this medicine, tell your doctor right away.
Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine several days before having surgery or medical tests.
Check with your doctor immediately if you have diarrhea, fever, or any symptoms of an infection.
This medicine may cause skin necrosis or gangrene. Call your doctor right away if you have pain, a color change, or a temperature change to any area of your body. Call your doctor right away if you have pain in your toes and they look purple or dark in color. These could be signs of a serious medical problem.
Calciphylaxis or calcium uremic arteriolopathy may occur in patients with or without end-stage kidney disease. Tell your doctor right away if you have purplish red, net-like, blotchy spots on the skin.
Warfarin may increase your risk of having kidney problems, including acute kidney injury. Check with your doctor right away if you have blood in the urine, decreased urine output, muscle twitching, nausea, rapid weight gain, seizures, stupor, swelling of the face, ankles, or hands, or unusual tiredness or weakness.
This medicine may increase your chance of bleeding. Check with your doctor right away if you notice any unusual bleeding or bruising, black, tarry stools, blood in the urine or stools, or pinpoint red spots on your skin. Avoid picking your nose. If you need to blow your nose, blow it gently.
Be careful when using a regular toothbrush, dental floss, or toothpick. Your medical doctor, dentist, or nurse may recommend other ways to clean your teeth and gums. Check with your medical doctor before having any dental work done.
Be careful not to cut yourself when you are using sharp objects, such as a safety razor or fingernail or toenail cutters. Avoid contact sports or other situations where bruising or injury could occur.
It is recommended that you carry identification that says you are using warfarin. If you have any questions about what kind of identification to carry, check with your doctor.
Do not take other medicines unless they have been discussed with your doctor. This includes prescription medicines, nonprescription (over-the-counter [OTC]) medicines, and herbal or vitamin supplements.
For healthcare professionals
Applies to warfarin: compounding powder, intravenous powder for injection, oral tablet.
General adverse events
The most common adverse reactions were fatal and nonfatal hemorrhage from any tissue or organ.[Ref]
Cardiovascular
- Frequency not reported: Hemorrhage, purple toes syndrome, infarction, systemic cholesterol microembolization, vasculitis, systemic atheroemboli[Ref]
Nervous system
- Frequency not reported: Cerebral hemorrhage, cerebral subdural hematoma, lethargy, headache, dizziness, taste perversion, paresthesia[Ref]
Gastrointestinal
- Frequency not reported: Gastrointestinal hemorrhage, rectal hemorrhage, hematemesis, pancreatitis, diarrhea, nausea, vomiting, melena, abdominal pain, cramping, flatulence, bloating[Ref]
Dermatologic
- Frequency not reported: Rash, alopecia, purpura, erythematous swollen skin patches, ecchymosis, skin necrosis, dermatitis, bullous eruptions, urticaria, pruritus[Ref]
Musculoskeletal
- Frequency not reported: Tissue necrosis, chills[Ref]
Metabolic
- Frequency not reported: Calciphylaxis, edema[Ref]
Respiratory
- Frequency not reported: Hemothorax, epistaxis, tracheal or tracheobronchial calcification[Ref]
Genitourinary
Hematologic
- Frequency not reported: Unexplained decrease in hematocrit, hemoglobin decreased[Ref]
Hepatic
- Frequency not reported: Jaundice, hepatic dysfunction, hepatitis, cholestatic hepatic injury, liver enzymes elevated[Ref]
Immunologic
- Frequency not reported: Hypersensitivity, allergic reactions, anaphylactic reactions[Ref]
Other
- Frequency not reported: Fever, fatigue, malaise, asthenia, pain, cold intolerance, feeling cold[Ref]
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References
1. (2001) "Product Information. Coumadin (warfarin)." DuPont Pharmaceuticals
2. Cerner Multum, Inc. "UK Summary of Product Characteristics."
3. Cerner Multum, Inc. "Australian Product Information."
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Further information
Warfarin side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.
