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Warfarin oral tablet side effects: A detailed guide

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Warfarin oral tablets are prescribed to treat or help prevent blood clots that may cause a stroke, heart attack, or death. Warfarin is a blood thinner that can cause mild or serious side effects, including major bleeding.
Medically reviewed by Dena Westphalen, PharmD
Updated on February 9, 2023

Specifically, the Food and Drug Administration (FDA) has approved warfarin oral tablets to:

This article describes possible side effects (also known as adverse effects) of warfarin oral tablets. You’ll also find information on cost savings and coupon options for warfarin.

Warfarin oral tablet is a generic version of the brand-name drug Jantoven. Warfarin also comes in an injectable form, but this form isn’t described in this article. To learn more about injectable warfarin, talk with your doctor.

You can explore this overview article to learn more about warfarin oral tablets, including the drug’s uses, dosage, ways to save on cost, and more.

Boxed warning: Risk of bleeding

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

For details, see the “Side effects of warfarin in detail” section below.

More common side effects of warfarin

Warfarin oral tablets may cause mild or serious side effects. Below are some of the more common side effects of this medication.

The most commonly reported side effect of warfarin oral tablets is unusual bleeding. The drug has a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of warfarin in detail” section below.

Mild side effects of warfarin

Warfarin oral tablets may cause certain mild side effects. Most often, mild side effects are temporary and can be easily managed. Tell your doctor or pharmacist if you have side effects that don’t go away or become bothersome.

Mild side effects of warfarin oral tablets that occurred in studies include:

Warfarin oral tablets may cause more mild side effects than those listed above. For details, see the drug’s prescribing information.

* To learn more about this side effect, see the “Side effects of warfarin in detail” section below.

Serious side effects of warfarin

Warfarin oral tablets may cause certain serious side effects. If you have any serious side effects from warfarin oral tablets, call your doctor right away. But if you think you’re having a medical emergency or your side effects feel life threatening, take immediate action. Call 911 or a local emergency number, or go to the nearest emergency room.

After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Visit MedWatch’s website if you’d like to notify the FDA about a side effect you’ve had with warfarin oral tablets.

Serious side effects of warfarin oral tablets that occurred in studies include:

* Warfarin oral tablet has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of warfarin in detail” section below.
† To learn more about this side effect, see the “Side effects of warfarin in detail” section below.

Common questions about side effects of warfarin

Here are answers to some common questions about side effects of warfarin oral tablets. If you have other questions, talk with your doctor or pharmacist.

Is weight gain or tiredness a side effect of warfarin?

No, weight gain and tiredness were not reported as side effects of warfarin oral tablets.

Sudden weight gain could be a sign of fluid building up in your body. This can be a symptom of a heart, liver, or kidney problem. Fluid buildup can also occur due to the condition you’re taking warfarin to treat.

Talk with your doctor if you have unexpectedly gained weight, have any swelling, or feel constantly tired while taking warfarin.

Can warfarin cause eye-related side effects?

Warfarin oral tablets aren’t known to cause eye-related side effects. These were not reported in studies of the drug. But people who took warfarin and had cataract surgery had an increased risk of minor complications. (Cataract surgery is used to treat cataracts, which is clouding of your eye lens.)

If you take warfarin, talk with your doctor before having eye surgery.

Does warfarin cause long-term side effects?

Warfarin oral tablets may cause long-term side effects. People who take warfarin for a long period of time have an increased risk of bleeding.* Other side effects, such as liver inflammation (swelling), may last for a long time if left untreated.

Tell your doctor if you experience any side effects while taking warfarin.

* Warfarin oral tablet has a boxed warning for this side effect. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). To learn more, see the “Side effects of warfarin in detail” section below.

Are memory problems a side effect of warfarin?

No, memory problems were not reported as a side effect in studies of warfarin oral tablets.

Memory problems can be due to several conditions, such as an infection, heart disease, an electrolyte imbalance, or a stroke. Warfarin is sometimes used as a treatment for some of these conditions.

Talk with your doctor if you are experiencing memory problems.

What are the overdose symptoms of warfarin?

Taking too much warfarin can cause major bleeding,* which may be fatal. Do not take more warfarin than what your doctor prescribes.

Symptoms of major bleeding may include:

  • bleeding that does not slow down when pressure is applied
  • blood that is soaking through multiple bandages
  • blood that is spurting out of a wound
  • bright red urine or black or bloody stools

If you think you’ve overdosed on warfarin, call your doctor immediately. If you believe your condition is severe or life threatening, call 911 or your local emergency number.

Ask your doctor when you may need to call for emergency medical help due to a warfarin overdose.

* Warfarin oral tablet has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of warfarin in detail” section below.

Coupon for warfarin

Visit this page to access Optum Perks coupons and get price estimates for warfarin when you use the coupons. These coupons can provide significant savings on your prescription costs.

Note: Optum Perks coupons cannot be used with any insurance copays or benefits.

Side effects of warfarin in detail

Below you’ll find details on some of the side effects of warfarin oral tablets.

Risk of bleeding

Warfarin has a boxed warning for the risk of bleeding. This is a serious warning from the Food and Drug Administration (FDA). In rare cases, bleeding may be fatal. Bleeding was commonly reported in studies of warfarin.

Symptoms can include:

  • bleeding gums
  • nosebleeds
  • coughing up blood
  • vomiting blood
  • brown or pink urine
  • black or red stools
  • bleeding for longer than usual from a cut
  • heavier menstrual bleeding than usual or vaginal bleeding
  • bruising that’s unexplainable or growing in size

You may have an increased risk of bleeding if you:

  • just started taking warfarin or have been taking warfarin for a long time
  • are over age 65 years
  • have a history of certain medical conditions
  • have certain genetic factors
  • take certain other medications

Ways to manage

Tell your doctor right away if you have any unusual bleeding. They’ll likely check how your blood is clotting and adjust your dose of the drug.

Your doctor will monitor you more closely while you take warfarin. This is to help lower your risk of bleeding.

Calcium buildup

Warfarin may cause calciphylaxis (calcium buildup in your blood vessels). This is a rare but serious side effect.

Signs can include:

Ways to manage

Tell your doctor if you experience any of the signs listed above. They can recommend the best treatment options for you.

Purple toes syndrome

Purple toes syndrome can occur with warfarin. With purple toe syndrome, you have pain and purple or dark coloring to your toes. This is an uncommon but serious side effect of warfarin.

Ways to manage

Tell your doctor right away if your toes hurt or start to turn purple or a dark color. If you have purple toes syndrome, your doctor will likely stop your warfarin and recommend a different medication to treat your condition.

Death of skin tissue

Death of skin tissue is a rare but serious side effect of warfarin. It can happen when blood clots stop the flow of blood through parts of your body. This prevents essential nutrients and oxygen from getting into tissue, causing tissue death.

Symptoms can include pain, skin color changes, or temperature changes in any area of skin on your body.

Ways to manage

Tell your doctor if you have any of the above symptoms so they can investigate and treat the skin tissue if needed. If you have skin tissue death, your doctor will likely stop your warfarin treatment and recommend a different medication to treat your condition.

Allergic reaction

For some people, warfarin oral tablets can cause an allergic reaction. This was rarely reported in studies of the drug.

Symptoms can be mild or serious, and they may include:

  • itchiness
  • skin rash
  • swelling under the skin, usually affecting eyelids, lips, hands, or feet
  • swelling of the mouth, tongue, or throat, which can make it hard to breathe
  • flushing (temporary warmth, redness, or deepening of skin color)

Ways to manage

For mild allergic reaction symptoms, such as a mild rash, call your doctor right away. They may recommend treatments to help manage your symptoms. They’ll also let you know whether you should keep taking the medication.

For severe allergic reaction symptoms, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms require immediate medical care because they can become life threatening.

If you’ve had a serious allergic reaction to warfarin oral tablets, your doctor may recommend taking a different medication instead.

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Warnings for warfarin

Below are some factors you may want to discuss with your doctor before taking warfarin oral tablets.

Boxed warning: Risk of bleeding

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

For details, see the “Side effects of warfarin in detail” section above.

Other warnings

It may not be safe for you to take warfarin oral tablets if you have specific health conditions. These are sometimes called drug-condition interactions. Other things may also affect whether warfarin oral tablet is safe for you to take.

Before taking warfarin oral tablets, tell your doctor about your health and medications you take. Things to consider include those listed below.

Low platelet level after taking heparin. If you take heparin (another blood thinner), it may lower your platelet level. If you have a condition that causes a low platelet level, you may have an increased risk of skin tissue death or gangrene if you start taking warfarin. Due to this risk, your doctor may not prescribe you warfarin until your platelets return to a usual level.

Kidney disease. If you have kidney disease, you may have an increased risk of calciphylaxis (calcium buildup in your blood vessels). You could also have an increased risk of acute kidney disease. Talk with your doctor if you have kidney disease. They will determine whether warfarin is the best option for you.

Allergic reaction. If you’ve had an allergic reaction to warfarin oral tablet or any of its ingredients, your doctor will likely not prescribe this medication. Ask them about other medications that may be better options for you.

Warfarin and pregnancy

Warfarin may cause problems with fetal development (commonly known as birth defects) during pregnancy. Examples reported in studies include low birth weight and unusual formation of body parts and organs. Due to this risk, your doctor will likely not prescribe warfarin if you’re pregnant or are trying to become pregnant.

If you’re pregnant or trying to become pregnant, talk with your doctor about other medications that are safe for you.

Warfarin and breastfeeding

It’s unknown if warfarin passes into breast milk. If it does pass into breast milk, warfarin may cause harm to a child who is breastfed. Due to this risk, your doctor will likely not recommend taking warfarin if you’re breastfeeding.

In some cases, your doctor may recommend you take warfarin while breastfeeding. If so, tell your doctor and your child’s doctor if your child has any bleeding* or bruising. Your doctor may recommend a different medication to treat your condition.

* Warfarin oral tablet has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of warfarin in detail” section above.

Warfarin and alcohol

Warfarin oral tablets are not known to interact with alcohol. But alcohol can affect how your body breaks down warfarin. This could cause a buildup of warfarin in your body, which may cause side effects, including an increased risk of severe bleeding.*

If you’d like to drink alcohol, talk with your doctor about whether it’s safe to consume it while taking warfarin oral tablets.

* Warfarin oral tablet has a boxed warning for this side effect. A boxed warning is the most serious warning from the FDA. To learn more, see the “Side effects of warfarin in detail” section above.

What to ask your doctor

This article describes common and serious side effects of warfarin oral tablets. If your doctor prescribes this medication, they can discuss possible side effects with you. Let your doctor know if you have concerns or questions about this medication.

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

  • Does warfarin cause the same side effects as other blood thinners?
  • Can I take zinc and warfarin at the same time? Will this cause side effects?
  • Do I have an increased risk of side effects because of my other medical conditions or any other medications I take?

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.

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