What is Warfarin

What is Warfarin?

Warfarin is a medication which prevents blood clots from forming in your body. It helps prevent heart attacks and strokes. It is used to treat high blood pressure, pulmonary embolisms (blood clots in the lungs), thrombosis (clotting of blood vessels) and deep vein thrombosis (a clot that forms in the leg).

The drug is manufactured by Pfizer Inc., a pharmaceutical company based in New York City. Warfarin was originally made from the leaves of the Chinese sweet wormwood plant (artemisia vulgaris).

The drug was first discovered in a German lab in 1937.

The medication was initially used to kill rats, but now is used by humans to prevent deadly conditions. It is the most commonly used anticoagulant, or “blood thinner,” in the world. Anticoagulation is used to treat and prevent blood clots, which can lead to heart attacks, strokes and pulmonary embolisms.

The drug works by blocking Vitamin K from participating in the process that causes your blood to clot. For this reason, patients need to maintain a steady intake of Vitamin K in their diet. Common foods that contain high levels of the vitamin include cabbage, broccoli, brussels sprouts, green beans and peas.

People who take the medication should avoid these foods, as eating too much will actually counteract the drug’s intended effect.

Warfarin comes in tablet and liquid form. It is typically taken once a day, with the dose adjusted based on your body weight. It can take anywhere from four to seven days for the drug to build up to an effective level.

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Doctors will often recommend patients get blood work done before starting on the drug and then once a month while taking it to ensure the proper dosage is being administered.

The drug comes with a number of potential side effects, including:

Skin pain


Reduced feeling of sensitivity to heat and cold

Joint pain and swelling


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Bloated sensation in the abdomen

Excessive bruising


Vision problems, including double vision and loss of vision in one eye

Coughing up blood

Slowed heart rate

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Stomach pain

Breathing difficulties


Difficulty speaking or swallowing

Awareness of your heartbeat (palpitations)


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Weird dreams

If any of these symptoms persist or worsen, or if you notice any other unusual symptoms, it is important to see your doctor immediately.

Warfarin is an incredibly effective medication, but can cause life-threatening side effects. It is essential that you are aware of the risks and take the necessary precautions to avoid accidental overdose. It is also important that you strictly adhere to your doctor’s recommended dosage.

If you are concerned about your dosage or experience any side effects, do not hesitate to contact your physician.

There are a number of foods that can interact with Warfarin, and can increase the effects and danger to the patient. While you should always be mindful of the foods you eat while on Warfarin, it is especially important to avoid the following:

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In general, the interaction between alcohol and Warfarin can pose a serious health threat to patients. Alcohol can increase the effects and side effects of Warfarin, as well as decrease how well the drug works. Drinking alcohol while on Warfarin is typically not recommended.

Cranberries and cranberry juice

These foods can increase how much Warfarin in your body, increasing the effects and danger to the patient. If you are taking Warfarin, be sure to avoid cranberries and cranberry juice.

Garlic and onions

These foods can also increase how much Warfarin in your body.

If you are taking Warfarin, be sure to avoid garlic and onions.

Vitamin K

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High levels of Vitamin K can decrease how well Warfarin works in your body. Foods high in Vitamin K include broccoli, Brussels sprouts, cabbage, kale, and spinach.

Be sure to limit your consumption of these foods while on Warfarin. Your physician may also recommend you take a Vitamin K supplement while on the medication.

NSAID Pain Relievers

Some over-the-counter pain relievers, like ibuprofen (Motrin, Advil) and naproxen (Aleve), can increase the negative side effects of Warfarin. It is recommended that you avoid these pain relievers while on Warfarin and discuss other pain management options with your physician.

FDA Warnings

The FDA has required a number of warnings on the label of Warfarin to alert patients to serious risks and side effects. These include warnings that Warfarin:

Should not be used by patients with deep vein thrombosis, pulmonary embolism, recent stroke or heart attack, or unexplained hemorrhage.

Should not be used by women who are pregnant or may become pregnant, unless other drugs are not effective in treating the condition

If you experience any of these serious side effects, stop taking Warfarin and contact your doctor immediately or seek immediate medical attention:

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Blood in vomit

Blood in urine

Black, tarry stools


Headaches that are severe

Shortness of breath

Slurring of speech

Sudden loss of vision or double vision

Swelling in your arms, face or legs

Unusual bruising or bleeding from minor cuts

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Yellowing of the skin or eyes

Other Side Effects and Warnings

The following are other side effects that have been associated with Warfarin. These are less serious, but should be reported to your physician immediately:

Allergic reactions including hives, itching, facial swelling, wheezing, and shock

Bleeding that will not stop

Tremor or uncontrollable shaking

Difficulty speaking

Extreme fatigue (weakness, tiredness)

Inability to move your legs

Swelling in the arms or legs

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If you experience any of these less serious side effects, also report them to your physician:



Dizziness or light-headedness




Nausea or vomiting

Skin rash, itching, or hives

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Stomach pain or cramps

Trouble concentrating

Unusual excitement, nervousness or anxiety

Yellowing of the skin or eyes

It is also important to note that Warfarin should not be taken with other blood thinners, such as heparin, clopidogrel (Plavix), dipyridamole (Persantine), and many other prescription drugs. These combinations greatly increased bleeding risk.

It is also recommended that you avoid alcohol while on Warfarin. Alcohol can increase the negative effects of the drug and may also lead to increased bleeding.

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High doses of Vitamin E and other supplements such as ginkgo biloba may also increase bleeding risk when taken with Warfarin.

If you are going to have surgery or dental work, talk to your physician about stopping Warfarin a few days before the procedure. Stopping the drug suddenly is not recommended and can increase the risk of bleeding.

If you believe that you may be pregnant, do not take Warfarin.

Do not change the dose of Warfarin on your own. Always consult with a medical professional to prevent complications.

Do not stop taking Warfarin, or change your dosage without first talking to your physician. Even stopping the drug for a short period of time can cause serious side effects.

Do not take any over-the-counter medications (including flea or tick medication for your pets) without first talking to your physician. Many of these contain ingredients that may increase the risk of bleeding while taking Warfarin.

If you experience any other side effects that concern you, make sure to discuss them with your physician.

NOTE: You must complete the full course of medication to make sure that your condition is no longer being affected by clots. Stopping treatment early can be dangerous.

What Conditions is Warfarin Used For?

Warfarin is used to treat and prevent blood clots. The medication prevents clots from forming or growing larger in your blood. This is important because when clots form in blood vessels they can cause death of the tissue in that area. For example, a clot in the brain can cause a stroke. A clot that forms in the lungs can cause death if not treated immediately.

There are many factors that affect your risk of forming a clot. Age is a major factor. Women generally have a greater risk of forming blood clots than men because of biological and lifestyle factors.

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Certain conditions can also increase your risk of having a blood clot. These include:

Recent surgery or injury

Having had a previous blood clot

Heart disease

Pulmonary Embolism (PE) – this is when an artery in your lungs is blocked by a clot


Certain cancers

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Use of an implanted medical device, such as a heart pump or dialysis machine

Using an electric blanket

Traveling for long periods of time in a vehicle, airplane or boat


Using birth control pills or device, or hormone replacement therapy


Use of an IUD (Intra-Uterine Device) for birth control

Menopause (if you are over 55)


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Elevated cholesterol levels

Warfarin is also used to prevent the clotting of blood in donor organs.

How Long Does it Take for Warfarin to Work?

Most people will begin to see an effect in one to two days after starting the medication. The medication will reach it’s full effect in three to seven days.

NOTE: It can take up to two weeks for your blood levels to become the correct amount of Warfarin in your body. During this time you may need to have your dosage adjusted. Make sure to tell your physician if you experience any bruising or bleeding during this time.

What are the Possible Side Effects of Warfarin?

All medications have side effects. The key is weighing the benefits of the drug versus the side effects. The following are some of the more common side effects of Warfarin (note: this isn’t a complete list).

Skin rash


Difficulty Breathing

Bruising or bleeding more easily than normal

Unusual vaginal bleeding (in females)

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Mood changes

Difficulty talking




Slurred speech

Muscle weakness

Severe abdominal pain

Difficulty swallowing

Painful or difficult urination

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If you experience any of these or notice anything else that concerns you, make sure to discuss it with your physician.

NOTE: Side effects vary for each individual. The above side effects are based on several patients that have taken Warfarin. Your experience with the medication may be different.

What are the Possible Interactions with Other Medications?

There are several medications that can interact with Warfarin. Make sure to tell all of your healthcare providers about every prescription and over the counter medicine you are taking. This includes herbs and supplements. Be aware that herbal medicines and supplements can sometimes have an effect on the way Western medications work, same with Western medications having an effect on herbal remedies.

Some of the medications that may interact with Warfarin include:

Anticoagulants such as acenocouberol and phenindione

Birth control pills, patches or rings containing estrogen and/or progestin

Diabetes medications including Glipizide, Glimepiride, Tolazamide and Tolbutamide

Antibiotics such as Cephalexin, Ciprofloxacin and Norfloxacin

Antiviral medication such as Delavirdine, Efavirenz, Lopinavir and Ritonavir

Antifungals such as Ketoconazole, Itraconazole and Fluconazole

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Stinging Nettles (Herbal Remedy)

Alcohol (especially when taken with methopheline)


If you experience any of the following symptoms while taking Warfarin, contact your physician immediately:



Skin Rashes


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Difficulty Breathing


Severe Itching of the Skin

Swelling of the Face, Lips or Tongue

Difficulty Swallowing

Chest Pain

Shortness of Breath



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Loss of Appetite

Nausea or Vomiting

Decreased Urination

Weight Gain


Stomach or Chest Pain

Dark Urine

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Yellowing of the Skin or Eyes

How Do I Store Warfarin?

Keep out of reach of children.

Do not allow anyone else to take your medication.

Store in a cool dry place, away from direct sunlight.

What Should I Do If I Forgot to Take a Dose?

Take the missed dose as soon as you remember. If you are closer to the time of your next dose, then skip the missed dose and continue your regular dosing schedule. Do not take a double dose.

What Should I Do If I Overdose?

If you or anyone else accidentally takes too much Warfarin, immediately contact the Poison Control Center at 1-800-222-1222.

What Should I Do If I Miss a Dose?

If you miss a dose, take it as soon as you remember. If you are close to your next dose, then skip the one you missed and resume your normal dosing schedule. Do not take a double dose unless otherwise directed by your physician.

What Should I Do If I Lose My Prescription Bottle?

We are required to have a record of your prescription on file. Call our office at 555-555-1212 to provide an alternative contact method or refill information in case your bottle is lost.

What Should I Do If I Have Further Questions About My Medication?

If you have questions, call your physician. If you experience any problems with your medication, contact your physician immediately.

Sources & references used in this article:

Kennedy’s Disease Symptoms

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