Warfarin Clathrateform

Introduction

Written by Patricia Weiser, PharmD
Medically reviewed by Rosanna Sutherby, PharmD
Updated on July 25, 2023

Warfarin (WAR far in) is a generic medication prescribed to help prevent blood clots. Warfarin belongs to a group of drugs called anticoagulants, commonly called blood thinners.

Specifically, the Food and Drug Administration (FDA) has approved warfarin for use in adults to help:

• prevent blood clots in the veins and lungs
• prevent blood clots related to atrial fibrillation (a type of heart rhythm problem) or heart valve replacement
• reduce the risk of heart attack, stroke, or death following a heart attack

Boxed warning: Risk of bleeding

Warfarin has a boxed warning about the risk of bleeding. Boxed warnings are the most serious warnings from the FDA.

Taking warfarin may cause bleeding that can be serious or even fatal in rare cases. Due to this risk, your doctor will monitor your international normalized ratio (INR) regularly throughout your warfarin treatment. These are blood tests that help you and your doctor determine how well warfarin is working.

INR results can also inform your doctor about your risk of bleeding. Your doctor may adjust your dosage of warfarin based on your INR results.

For details, see the “Interactions and warnings for warfarin” section.

Side effects of warfarin

Warfarin may cause mild or serious side effects. More common mild side effects of warfarin and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about warfarin’s side effects, see this article or ask your doctor or pharmacist. You can also refer to the prescribing information for warfarin listed in the “Resources” section.

Mild side effects

More common mild side effects reported with some forms of warfarin are listed below.

To learn more about warfarin’s side effects, refer to the prescribing information for warfarin listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Warfarin oral tablet’s mild side effects include:

• mild bleeding, such as minor nosebleeds
• bruising
• digestive problems, such as nausea, diarrhea, and abdominal pain
• hair loss
• mild allergic reaction*

* For details about this side effect, see the “Interactions and warnings for warfarin” section.

Serious side effects

Serious side effects of warfarin are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about warfarin’s side effects, refer to the prescribing information for warfarin listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, warfarin’s serious side effects include:

• damage or death of skin tissue
• damage to small blood vessels due to a buildup of calcium deposits
• boxed warning: risk of bleeding*
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for warfarin” section.

Common questions about warfarin

Below you’ll find answers to a few commonly asked questions about warfarin.

What is warfarin’s mechanism of action? How does the drug work?

Warfarin is prescribed to help prevent blood clots. Blood clots occur when substances called clotting factors clump together. Clotting factors work in a stepwise process, similar to a “domino effect.” The body depends on vitamin K to make certain clotting factors.

Warfarin works by reducing the amount of vitamin K in your body. Without enough vitamin K, the body can’t make certain clotting factors. Warfarin interrupts the body’s stepwise clotting process, which helps prevent blood clots.

The body naturally makes vitamin K, but it’s also found in certain foods. To learn about foods that interact with warfarin, see the next question. You can also talk with your doctor or pharmacist.

Warfarin starts working within 24 hours, but it takes about 4–5 days to reach its full effects in your body. In some cases, doctors temporarily prescribe a different anticoagulant medication until warfarin becomes fully effective.

Talk with your doctor or pharmacist if you have questions about how warfarin works.

Do I need to make changes to my diet while taking warfarin?

Possibly. Certain foods can interact with warfarin in different ways. Some foods should be avoided, while others are safe if you follow certain guidelines.

Foods and beverages to avoid while taking warfarin include green tea, grapefruit, grapefruit juice, cranberries, cranberry juice, and alcohol.

Foods that are rich in vitamin K are acceptable to eat while taking warfarin if you consume them in around the same amount each day. Making drastic changes to your intake of these foods can affect how warfarin works. Examples of foods that contain high amounts of vitamin K include:

• spinach
• brussels sprouts
• collard greens
• green lettuce
• kale

Talk with your doctor before making drastic changes to your diet while taking warfarin.

Does warfarin affect my INR?

Yes, it does. Taking warfarin may cause bleeding that can be serious or even fatal in rare cases. Warfarin has a boxed warning about the risk of bleeding. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

Due to this risk, your doctor will monitor you with prothrombin time tests. Doctors use these tests to determine your international normalized ratio (INR). The results can inform your doctor about your risk of bleeding.

Your doctor will monitor your INR throughout your treatment with warfarin. These blood tests help you and your doctor determine how well warfarin is working. Your doctor may adjust your dosage based on your INR results.

Your INR results can be affected by certain factors, such as diet changes. One example is if you drastically increase your intake of foods that contain vitamin K, such as green, leafy vegetables. In this case, your doctor may need to adjust your dosage of warfarin.

Talk with your doctor to learn how often you’ll need blood tests while taking warfarin. You should also consult with them if you’re considering making drastic changes to your diet.

Uses of warfarin

The Food and Drug Administration (FDA) approves prescription drugs such as warfarin for certain conditions. Approved uses for warfarin are described below.

Use for blood clots

Doctors may prescribe warfarin oral tablet to help prevent blood clots. It’s prescribed for this purpose in certain adults. It’s usually prescribed as a long-term treatment.

Specifically, the FDA has approved warfarin for use in adults to help:

• prevent blood clots from forming in the veins that can then travel to the lungs
• prevent blood clots related to atrial fibrillation (a type of heart rhythm problem) or heart valve replacement
• reduce the risk of heart attack, stroke, or death following a heart attack

Blood clots can form in your veins and prevent blood from flowing to your tissues and organs. This can lead to serious problems, such as heart attack and stroke, which may be life threatening. Symptoms of blood clots can include:

• pain and swelling in your arm or leg
• warmth or discoloration of your arm or leg
• difficulty breathing
• chest pain

In certain situations, doctors may prescribe warfarin together with aspirin.

Doctors may not prescribe warfarin oral tablet in certain situations. For example, warfarin isn’t prescribed to treat a blood clot that’s already formed. It also isn’t prescribed to help treat body tissues that are already damaged due to a lack of blood flow caused by a clot.

Interactions and warnings for warfarin

Below, you’ll find information about warfarin’s possible interactions and warnings.

Interactions of warfarin

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take warfarin, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for warfarin” section below.

Warnings for warfarin

Some people should not take warfarin, and others should take it cautiously.

Boxed warning: Risk of bleeding

Warfarin has a boxed warning about the risk of bleeding. Boxed warnings are the most serious warnings from the Food and Drug Administration (FDA).

Warfarin works to help prevent blood clots. Because of how the drug works to help prevent clots, warfarin can cause bleeding as a side effect. Bleeding was commonly reported in studies of warfarin.

Bleeding with warfarin can range from minor to serious and even fatal. Symptoms of bleeding issues may include bruising easily, bleeding gums when you brush or floss your teeth, nosebleeds, vomiting blood, blood in your stool, or bleeding more or longer than usual after a minor injury.

To reduce your risk of bleeding while taking warfarin, you’ll get blood tests on a regular basis. The results of these blood tests inform your doctor about your risk of bleeding. Your doctor will use this information to adjust your dosage of the drug if needed.

If you experience minor bleeding, tell your doctor. They’ll likely adjust your dosage of warfarin. If you have bleeding that won’t stop or seems severe, call 911 or the local emergency number or seek emergency medical care right away.

To learn more, talk with your doctor or pharmacist.

Other warnings

Warfarin could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether warfarin is a safe option for you. These warnings may differ based on the form of warfarin you take.

Ask your doctor about specific warnings for warfarin, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Warfarin can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to warfarin or any of its ingredients, your doctor will likely not prescribe warfarin. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to warfarin, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of warfarin

If you take warfarin by mouth, you should not take more warfarin than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much warfarin, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and warfarin

Information about warfarin and pregnancy and breastfeeding is described below.

Warfarin and pregnancy

Warfarin should not be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication. Your doctor may suggest birth control options to use during treatment with warfarin.

One exception is that doctors may prescribe warfarin during pregnancy if you have a mechanical heart valve and are at high risk of developing blood clots.

If you’re planning a pregnancy or can become pregnant, talk with your doctor about blood clot treatment or prevention options during pregnancy. Together, you can discuss the risks and benefits of your treatment options and decide whether you should take warfarin during pregnancy.

Warfarin and breastfeeding

There are risks to taking warfarin while breastfeeding. But there are also risks associated with having untreated blood clots during this time. (Keep in mind that warfarin is prescribed for treating and helping prevent blood clots.)

For instance, warfarin may cause bruising or bleeding in a child exposed to the drug through breast milk.

If you’re planning to breastfeed, talk with your doctor about your treatment options. Together, you can discuss the risks and benefits of your treatment options and decide whether you should take warfarin during this time. Your doctor may recommend other healthy ways to feed your child.

What to ask your doctor

Let your doctor know if you have questions about warfarin or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• How does warfarin compare with other medications, such as Xarelto?
• Am I at higher risk of side effects of warfarin than others?
• What over-the-counter cold and cough medications can I safely take while taking warfarin?

Resources

• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm
• Warfarin sodium tablets (crystalline), for oral use. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/c41b7c23-8053-428a-ac1d-8395e714c2f1/spl-doc

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.