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Warfarin: 12 Facts You Need to Know About This Blood Thinner

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Jan 12, 2022.

Warfarin: Is It A Safe Generic?

The year was 1954. Coumadin, a widely used blood-thinner, medically known as an anticoagulant, was approved to help prevent potentially deadly blood clots in the heart, lungs, veins, and arteries.

Warfarin, the more affordable generic form, became available years later, but concerns arose about the safety of switching between the brand and generic. Some patients, and even doctors, were afraid to switch. However, studies have shown there are few, if any, risks of using generic warfarin.

  • But you still need to keep up with your blood tests to help monitor for its effectiveness and safety.
  • Your doctor may schedule more frequent monitoring when you first switch to a generic product to monitor your individual response.
  • Small dose adjustments may be needed until blood levels remain in the target range, but this is normal for most patients.

Today, most patients use the generic warfarin from the outset. The brand product Coumadin is now discontinued, but another affordable warfarin called Jantoven is available at the pharmacy.

Color-Coded for Safety

Warfarin is considered a high-alert drug by the Institute for Safe Medication Practices (ISMP), meaning it can cause serious injury. Therefore, it is very important for you to know about this blood thinner and take it exactly as directed.

Generic warfarin tablets may come in different shapes, but each strength comes in just one color.

  • For example, the 5 milligram (mg) tablet, one of the most common strengths, comes in a peach/light orange color.
  • To help prevent confusion, it's always a peach/light orange color, no matter the manufacturer; however, the tablet shape and imprints may vary.
  • With other generic medications, colors, shapes and imprints can and do change frequently.

Before you leave the pharmacy, make sure the color of your tablets match the strength your doctor prescribed. If you have questions, speak directly with the pharmacist. Taking the wrong dose may lead to dangerous clots or excessive bleeding.

Still concerned? You can also use the Pill Identifier Wizard to verify medications.

Mixing with Vitamins, Herbals and Natural Supplements

Warfarin drug interactions deserve your attention.

For example, the nonprescription herbal St. John's Wort, sometimes used to help with mild depression, reduces the effectiveness of warfarin by boosting production of enzymes that break down warfarin.

Examples of other supplements that may interact with warfarin include:

Check with your doctor before you combine any over-the-counter medicine, vitamin, herbal product or supplement with warfarin.

Warfarin: Some Food and Drinks Can Interact

Most people who take warfarin are aware that eating green, leafy vegetables like spinach, kale, or turnip greens may affect the blood thinning ability of warfarin. These foods contain vitamin K that can block warfarin action.

However, did you know that other foods or beverages may affect the therapeutic action of your warfarin, too? These can include:

In general, diets should remain consistent while taking warfarin. Always follow the labeling on your prescription and ask your doctor or pharmacist if you have questions about any food or beverages.

Bleeding Risk Precautions

While on warfarin, you might bleed more easily, so it's important to take precautions.

  • For example, use a soft toothbrush, waxed dental floss, and an electric razor to avoid accidental cuts.
  • Avoid sharp objects; use caution in the kitchen.
  • Be wary of falling risks, like climbing a ladder or walking on slick sidewalks.

Many prescription drugs can interact with warfarin. Even common over-the-counter (OTC) drugs may have an effect, such as:

It's worth your time to have a drug interaction review performed by your pharmacist with each new prescription, OTC, herbal or vitamin supplement.

Vitamin K to the Rescue

No doubt many patients are nervous about taking a blood thinner. However, one advantage of using warfarin is that bleeding events can be reversed with the use of Vitamin K. In fact, it's the vitamin K you were told to be wary of in green, leafy vegetables -- but in medication form.

Other reversal agents have now been approved for the newer direct-acting oral anticoagulants.

And what if you have a serious bleeding episode while on a blood-thinning medication? Should you stop it all together? Ultimately, your doctor will help guide you to the best agent for your needs.

  • A clinical study published in Stroke suggests that most people will benefit from restarting their blood thinning medication to help prevent clots and lower the risk of stroke and heart attacks.
  • The researchers also found that Pradaxa (dabigatran) may be less likely than warfarin to cause recurrent bleeding.

Warfarin: Not a Friend to Rodents

Warfarin may be a life-saving drug for you, but it's a killer for rats. In fact, warfarin was the first anticoagulant "rodenticide".

Rodenticides are pesticides that kill rodents. Warfarin was used widely as a rodenticide, but today it's use is declining as many rodents have grown resistant to it.

Rodents include not only rats and mice, but also squirrels, woodchucks, chipmunks, porcupines, nutria, and beavers. As in humans, warfarin use stops normal blood clotting in rodents. Although rodents play important roles in nature, they can carry disease and may sometimes require control.

Problem: Birds of Prey Getting a Full Warfarin Dose

Killing rats and other rodents with warfarin rodent poison led to a problem, the death of birds of prey like eagles, owls and hawks. These birds of prey hunt and eat the rodents that have ingested the poison.

In fact, North American lawmakers moved to restrict the use of rodent poisons based on blood thinners, as studies show that the toxins accumulate in birds of prey and other animals.

Another problem? Rodent traps containing poison left outside can be consumed by other animals -- and in the worse case scenario -- a child might get their hands on it.

Painful Purple Toes

Purple Toe Syndrome may sound like a by-product of wearing high-heels, but it's actually a fairly rare complication associated with early warfarin use, usually within the first 3 to 8 weeks of treatment.

This condition is thought to be due to small emboli (blood clots) in the blood vessels which cause a purple color in the toes and feet. Other symptoms include:

  • a cold feeling in the feet
  • pain
  • possible sloughing off of the skin (necrosis).

Typically, warfarin therapy is stopped with this diagnosis and another type of anticoagulant will be substituted. Check with your doctor immediately if these symptoms appear.

(Not So) Happy Hour

Warfarin is notorious for it's food and drug interactions, and that includes alcoholic beverages.

  • Excessive use of large amounts of alcohol is known to affect how warfarin breaks down in your body (known as drug metabolism) and can increase the risk of bleeding.
  • Alternatively, in patients with liver disease (for example, cirrhosis) who abuse alcohol chronically, the risk for a blood clot may increase.

The bottom line? In general, avoid large amounts of alcohol. Moderate consumption (1 to 2 drinks per day) are not likely to affect the response to the anticoagulant in patients with normal liver function, but always check with your doctor for a recommedation specific for you.

Call your doctor promptly if you have any unusual bleeding, bruising, vomiting, blood in your urine or stools, headache, or feel dizzy or weak.

Is Your Blood Really Thinner with Warfarin?

Warfarin is often referred to as a "blood thinner," but this is a misnomer because warfarin (and other coagulation modifiers) do not actually "thin" the blood.

So what happens?

  • When you cut yourself, there is a series of clotting factors found in your blood that help to form a blood clot to stop the bleeding.
  • Warfarin actually blocks (inhibits) these vitamin K-dependent clotting factors and other proteins to keep the blood anti-coagulated ("thin").
  • That's also why vitamin K can be given to stop excessive bleeding when it occurs during warfarin treatment.

Warfarin: A Cost-Saving Generic

Many patients are being switched from warfarin to a newer generation of anticoagulants called direct-acting oral anticoagulants. This new class protects well against blood clots, but can be more expensive. Examples you may have heard of include Xarelto and Eliquis.

For some patients, their insurance will pay for the more expensive drug, and -- a big plus -- no regular blood tests are required with these newer agents. But for patients who have limited or no insurance, these new, more expensive drugs can be a hardship.

  • Generic warfarin runs about $4.00 to $8.00 for a month's supply at many retail pharmacies, but if you have to pay for the blood tests, too, that could add up quickly.
  • Talk to your doctor about the best option if you require a life-saving blood thinner, say for atrial fibrillation or a deep vein thrombosis (DVT).

Learn More: Generic Drug FAQs

Finished: Warfarin: 12 Facts You Need to Know About This Blood Thinner

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  • Institute for Safe Medication Practices (ISMP). Warfarin (Consumer Med Safety) Accessed Jan. 12, 2022 at
  • Connolly S, et al. Dabigatran versus Warfarin in Patients with Atrial Fibrillation. N Engl J Med 2009; 361:1139-1151. Accessed Jan. 27, 2021 at DOI: 10.1056/NEJMoa0905561
  • Dentali F1, Donadini MP, Clark N, et al. Brand name versus generic warfarin: a systematic review of the literature. Pharmacotherapy. 2011 Apr;31(4):386-93. doi: 10.1592/phco.31.4.386. Accessed Jan. 27, 2021 at PMID: 21449627 DOI: 10.1592/phco.31.4.386
  • Witt DM, Tillman DJ, Evans CM, at al. Evaluation of the clinical and economic impact of a brand name-to-generic warfarin sodium conversion program. Pharmacotherapy. 2003 Mar;23(3):360-8. Accessed Jan. 12, 2022 at PMID: 12627935 DOI: 10.1592/phco.23.3.360.32103
  • Pereira JA1, Holbrook AM, Dolovich L, et al. Are brand-name and generic warfarin interchangeable? Multiple n-of-1 randomized, crossover trials. Ann Pharmacother. 2005 Jul-Aug;39(7-8):1188-93. Epub 2005 May 24. Accessed Jan. 12, 2021 at doi: 10.1345/aph.1G003. Epub 2005 May 24. PMID: 15914517

Further information

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