Warfarin Side Effects

Publication Date: 
Tue, 11/08/2011
By: Alere Staff

Every drug has the potential for side effects, an unwanted or an unexpected action of a product. Some are minor, others more serious. Patients taking warfarin (or brand of warfarin such as Coumadin®) need to be aware of some of the more serious side effects.

Warfarin is in the category of “black box” warning drugs. These drugs have life-threatening risks requiring manufacturers to put warnings about their product in a black box in the package insert. The package insert is an U.S. Food and Drug Administration (FDA) required document explaining the clinical pharmacology, metabolism, indications, contraindications, warnings, adverse reactions, over-dosage, dosing and administration and how the medication is supplied.

The most serious risk of warfarin is bleeding in any tissue or organs. Bleeding risk is associated with the intensity of warfarin. Warfarin dosing is highly individualized, meaning each patient is specific in his or her needs of safe and effective dosing. Increasing the dose and duration of warfarin increases the risk of bleeding. The higher the International Normalized Ratio (INR), the greater the severity of the bleeding event if one occurs.1

Purple toe syndrome is also associated with warfarin treatment, normally occurring within the first 3-10 weeks although this condition is extremely rare (<0.1%). Purple toe syndrome is caused by localized thrombosis and characterized by dark, purplish color of the toes. The condition is reversible but left untreated can lead to gangrene and, in extreme cases, amputation.

Other side effects reported with warfarin use include hair loss, nausea, vomiting, cramping or diarrhea, although these are very rare and may be associated with other conditions or other medication use.

Many common complaints from patients on warfarin are associated with the natural aging process. Complaints of fatigue are common but not associated with warfarin therapy. Most patients taking warfarin are on many other medications which carry their own side effects. Patients should communicate any side effects (expected or otherwise) with their health care providers.

Bleeding is the most common side of warfarin therapy and related to controlling INR test results. Patients remaining in their target range are not much more at risk than patients of the same age not on warfarin. More frequent home testing has been shown to decrease the risk of major bleeding by 55% than those testing in traditional, monthly testing environments.2

The benefits offered by warfarin include the prevention of stroke or heart attack. The risk of bleeding is real, but manageable.

  1. Bristol-Myers Squibb Company. Medication Guide for Coumadin Tablets and Coumadin for Injection [Package Insert]. Princeton, NJ: Bristol-Myers Squibb Company. 2009.

  2. Heneghan C., et al. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. The Lancet. 2006. 367, 404-11.



COUMADIN® is a registered trademark of Bristol-Myers Squibb Pharma Company. Alere is not affiliated or associated with Bristol-Myers Squibb Pharma Company or the COUMADIN® trademark.