Warfarin (name brands include: Coumadin, Jantoven, Lawarin, Marevan, Waran, and Warfant) is an anticoagulant prescribed to patients needing to reduce and prevent blood clot formations. It is prescribed to more than 2 million people each year to prevent heart attacks, strokes, and blood clots.1
The beginnings of Warfarin occurred during the late 1920s when cattle from the U.S. and Canada began bleeding to death from a mysterious ailment. Over the next two decades researchers were able to pinpoint clover mold called Dicumarol as the culprit. The raw form of Dicumarol causes extreme bleeding, hemorrhaging and death and because of this it was synthetically altered to function as a rodenticide. The rat poison patented as “Warfarin” was used during the 1940s and 1950s.
Thought to be harmful to humans, Warfarin was not deemed safe for use until 1951 when a man from the U.S military unsuccessfully attempted suicide by ingesting mass quantities of the rat poison. This incident triggered doctors and researchers to reevaluate the use of Warfarin in humans.2 Since then Warfarin has become one of the most prescribed drugs in the U.S.
How Warfarin Works
Blood forms clots in the human body from proteins that your liver produces from the Vitamin K you ingest. Warfarin works by inhibiting certain enzymes of Vitamin K and thus increasing the time it takes to form clots.
Who Uses Warfarin
Warfarin is primarily used to treat or prevent strokes and blood clots such as DVTs (deep vein thrombi of the legs) and PEs (pulmonary embolism of the lungs). Warfarin is also prescribed to people who have medical conditions such as irregular heartbeat, heart valves issues, and heart attacks.
Patients taking Warfarin require frequent blood tests known as INRs. This test measures the thickness of the blood and determines if you are in a therapeutic range. Learn more about INR tests.
Warfarin Dosages Levels
Warfarin dosages vary greatly from person to person and are usually not impacted by physical characteristics such as weight and height. Your doctor will prescribe dosages to you and adjust them based on your desired INR number; typically 2.0-3.0 or 2.5-3.5.
Warfarin comes in tablet form and is available in various strengths. See chart below.3
Warfarin is one of the most sensitive prescription drugs on the market. It interacts with a myriad of foods, beverages, and over the counter medicines. Learn more about Coumadin diets.
Warfarin Side Effects
The most important side effect of Warfarin is bleeding. If a person using warfarin injures themselves they may bleed considerably more than usual since Warfarin is designed to increase the time it takes to clot. Severe bleeding and black stool/rectal bleeding is something to watch for.
According to the Mayo Clinic, other Warfarin side effects include:4
- Skin conditions such as hives, a rash or itching
- Swelling of the face, throat, mouth, legs, feet or hands
- Bruising that comes about without an injury you remember
- Chest pain or pressure
- Nausea or vomiting
- Fever or flu-like symptoms
- Joint or muscle aches
- Difficulty moving
- Numbness or tingling in any part of your body
- Painful erection lasting four hours or longer
Although rare, Warfarin can also cause skin tissue death (necrosis) and gangrene requiring amputation. This complication most often happens three to eight days after you start taking Warfarin. If you notice any sores, changes in skin color or temperature, or severe pain on your skin, notify your doctor immediately.
Less serious Warfarin side effects to tell your doctor about:
- Feeling cold
- Pale skin
- Changes in the way foods taste
- Hair loss
Citations (view all)
- 1. US FDA, "FDA Approves Updated Warfarin (Coumadin) Prescribing Information." Last modified August 16, 2007. Accessed April 22, 2012. http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/2007/ucm108967.htm.
- 2. University of Wisconsin, Madison, "Warfarin: A Chapter in International Standardization of Therapeutic Practices beyond a Commercialized Drug." Last modified October 22-23, 2010. Accessed April 22, 2012. http://www.pharmacy.wisc.edu/sites/default/files/private/american-institute-history-pharmacy/AIHPconf2010.pdf.
- 3. University of Utah, "Taking Warfarin." Accessed April 22, 2012. http://healthcare.utah.edu/thrombosis/patients/warfarin/warfarin_guide_taking.html.
- 4. Mayo Clinic, "Warfarin side effects: Watch for interactions." Last modified Feb. 16, 2012. Accessed April 22, 2012. http://www.mayoclinic.com/health/warfarin-side-effects/HB00101.