Warfarin is an anticoagulant, often called a blood thinner. It prevents harmful blood clots. It needs regular blood tests, because the right dose varies from person to person.
What Is Warfarin Used For?
- Preventing stroke in atrial fibrillation
- Treating and preventing deep vein thrombosis and pulmonary embolism
- Preventing clots in people with mechanical heart valves
- Preventing clots after some heart attacks
How Does Warfarin Work?
Warfarin blocks vitamin K, which your liver needs to make clotting proteins. With fewer clotting proteins, your blood clots more slowly.
General Dosage Information
This is general information only. Your doctor sets the right dose for you, so follow your prescription and the label.
- Doctors set the dose using a blood test called the INR. Most people aim for an INR between 2 and 3, and people with mechanical valves may aim higher.
- Take it at the same time each day.
- If you miss a dose, take it the same day. Never take a double dose the next day.
Side Effects of Warfarin
Common Side Effects
- Easy bruising
- Bleeding gums or nosebleeds
- Heavier periods
Serious Side Effects
Call your doctor or get emergency help if you notice:
- Bleeding that does not stop
- Black or bloody stools, or vomiting blood
- Sudden severe headache, confusion, or weakness
- Red or brown urine
- A head injury or a bad fall, even if you feel fine
Who Should Be Cautious?
- Pregnant women, who should not take it
- People with liver or kidney disease
- Older adults and people at risk of falls
- People with a bleeding disorder or ulcers
Drug Interactions
Tell your doctor and pharmacist about every medicine and supplement you take. Examples of important interactions include:
- Antibiotics, antifungals, and amiodarone: they can raise the effect of warfarin.
- Aspirin and NSAIDs: they raise the risk of bleeding.
- Herbal products such as St. John’s wort, ginkgo, and garlic: they can change the effect.
- Alcohol: heavy drinking changes how warfarin works.
- Foods rich in vitamin K, such as spinach and kale: keep the amount you eat steady.
Storage and Precautions
- Store it at room temperature, away from heat, light, and moisture.
- Keep it out of the reach of children.
- Tell every doctor and dentist that you take warfarin, and carry a card or wear an alert band.
Frequently Asked Questions
Do I need to avoid green vegetables?
No. Eat a steady amount each week and do not change suddenly.
How often do I need blood tests?
Often at first, then every few weeks once your dose is stable.
Can I take painkillers?
Paracetamol is usually safer. Avoid NSAIDs unless your doctor says so.
Disclaimer: This article is for information only. It is not medical advice. Please talk to your doctor about your own health.