6 Warfarin Side Effects You Should Know About

Warfarin (Coumadin, Jantoven) is a well-known medication that treats and prevents unwanted blood clots. It belongs to a group of blood thinners called anticoagulants. And warfarin’s been saving lives since the 1950s.

Despite its clear benefits, there are side effects it’s good to be aware of when you’re taking warfarin. Some risks, such as bleeding, may be obvious. But others may be a bit more unexpected.

Warfarin side effects at a glance

Here’s a breakdown of the warfarin side effects you might come across. Keep in mind that it’s possible you may experience a side effect that isn’t listed here. So it’s best to check in with your warfarin care team about any side effects you experience while taking it.

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Mild warfarin side effects: 

• Minor Bleeding or Bruising

• Nausea and Vomiting

• Diarrhea

• Gas and bloating

• Taste changes

• Chills

• Itchy skin

Serious warfarin side effects:

• Severe bleeding

• Tissue death (necrosis)

• Calciphylaxis (calcium deposits in blood vessels)

• Kidney damage

• Vasculitis (inflamed blood vessels)

• Hair Loss

• Liver Problems

• Purple toe syndrome

• Serious skin reactions

Let’s look at six possible warfarin side effects in more detail. Knowing how to identify and manage side effects can help protect your safety and ensure you’re getting the most out of your treatment. 

1. Bleeding

Warfarin is a blood thinner. So it’s no surprise that bleeding is the most common — and the most serious — warfarin side effect. In most cases, bleeding is minor and easily managed at home. But it can also be severe, or even life-threatening, in some cases. 

Your warfarin care team will measure your international normalized ratio (INR) regularly while you’re taking warfarin. This helps them keep an eye on how thin your blood is and adjust your warfarin dosage if needed. Keeping these appointments can help protect you against bleeding-related side effects. And be sure to check with your warfarin care team about any changes to your medications. Drug interactions can also affect INR levels.

It’s also key to eat a consistent diet while you’re taking warfarin. Making large changes to what or how much you’re eating, especially the amount of vitamin K in your food, can also raise your risk of bleeding.

Minor Bleeding

Minor bleeding due to warfarin typically includes incidents such as nosebleeds, bruising more easily, and bleeding from the gums when brushing your teeth. Using a soft-bristle toothbrush and waxed dental floss can help prevent gum bleeding.

Bleeding is considered mild if it’s a small amount of blood and it stops on its own. But if it’s something new for you or it’s happening often, let your care team know. It could be a sign that your warfarin dose is too high.

Severe Bleeding

Severe bleeding is also a possible warfarin side effect. It’s not as common as mild bleeding, but it can be life-threatening if it’s not treated right away. Signs of serious bleeding include:

• Bleeding that doesn’t stop

• A bruise that continues to grow

• Blood in your urine (may look red or dark brown)

• Blood in your stool (can be either bright red or black, tarry stool)

• Heavy or unusual menstrual bleeding

• Coughing up or vomiting blood (may look like coffee grounds)

• Severe headache

• Vision or speech changes

Call 911 or seek emergency care right away if you notice any signs or symptoms of severe bleeding. And be sure to let the medical team know you’re taking warfarin. This will help them determine the best way to treat you.

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Good to know: If you have a fall or hit your head while taking warfarin, you should get checked out right away. Bleeding can happen inside your body after an impact, and you may not notice symptoms on your own. 

2. Gastrointestinal issues

Gastrointestinal (GI) issues, such as nausea and vomiting, diarrhea, and stomach pain, are possible warfarin side effects. You may also feel bloated or more gassy than usual. These symptoms can be unsettling, but they often go away as your body gets used to warfarin. Staying hydrated can help you feel better.

Try to keep a consistent diet in spite of GI side effects, if possible. As mentioned, changes to what you’re eating can affect how well warfarin works. If you’re unable to eat normally due to stomach issues, let your care team know. They may need to adjust your warfarin dosage until you’re feeling better.

If diarrhea lasts longer than 1 day, let your care team know. And if nausea is severe, or happens along with stomach pain and vomiting, seek medical care. These could be symptoms of internal bleeding.

3. Taste changes

It isn’t common, but an altered sense of taste is a possible warfarin side effect. You may notice food or drinks taste different than usual. This side effect can be bothersome, but it doesn’t seem to be a serious issue.

It’s possible your taste will return to normal with time. But if it doesn’t, or the changes are bothersome, let your healthcare team know. They can see if a different blood thinner is an option for you. 

4. Skin-related issues

Skin-related issues, such as bruising, rashes, and itchy skin, can happen while you’re taking warfarin.

Bruises or small, pinpoint brown or red spots called petechiae can occur due to mild bleeding under the skin. These aren’t usually serious, but if they worsen or don’t heal on their own, let your healthcare team know.

Your skin may also feel more itchy than usual. Dry skin treatments, such as creams or lotions, may help. But if you have itchy skin along with a rash, it’s best to have it looked at by a medical professional. If you’re also having trouble breathing, seek emergency care.

In rare cases, warfarin can cause vasculitis (inflamed blood vessels) and skin necrosis (tissue death). These conditions can lead to discolored, painful toes, often referred to as “purple toe syndrome.” But they can happen elsewhere on the body, too. 

Serious skin problems usually appear soon after starting warfarin. But they can also happen if you’ve been taking warfarin for a long time. They typically start with painful skin rashes or bruises that don’t heal and require prompt treatment.

Good to know: It can be hard to tell if skin issues are serious on your own. So it’s best to show your healthcare team any rashes or wounds that develop while you’re taking warfarin. They can determine the cause and the best treatment option before a more serious problem develops. 

5. Hair loss

Hair loss is another possible warfarin side effect. It’s not common, but it can be distressing. Unlike other side effects, you may not notice hair loss until you’ve been taking warfarin for several months, or even years. And it’s not clear why it happens.

If you’re noticing hair loss while taking warfarin, let your healthcare team know. Switching to a different blood thinner medication may help reverse it if that’s an option for you. 

6. Liver problems

Although rare, liver damage is a possible warfarin side effect. It usually appears in the first 3 to 8 weeks of treatment. And in most cases, it’s mild and goes away quickly once you stop taking warfarin.

Let your healthcare team know if you notice any symptoms of liver damage, including: 

• Fatigue

• Abdominal swelling or pain

• Clay-colored stools

• Yellowing of the skin or eyes (jaundice)

When should you seek medical care for warfarin side effects?

You should contact your healthcare team about any warfarin side effects that are bothersome or interfere with your normal routine. It’s also best to have them look at any rashes or changes to your skin that appear.

You’ll likely see a warfarin care team to monitor your INR on a regular basis. This is often a good time to go over any side effects you’re experiencing. Your care team can then make dose adjustments if needed. But you shouldn’t change your dose or stop taking warfarin on your own, even if side effects are troubling you. This can raise your risk of blood clots. 

Seek emergency medical care if you notice any signs of severe bleeding or liver damage while you’re taking warfarin.

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Written by:

Justin DeFlorian, PharmD, BCPS

Justin DeFlorian, PharmD, BCPS, is a board-certified clinical pharmacist. He received his Doctor of Pharmacy degree from the University of Wisconsin-Madison.

Edited by:

Stacia Woodcock, PharmD

Stacia Woodcock, PharmD, is a pharmacy editor for GoodRx. She earned her Doctor of Pharmacy degree from the University of Kentucky and is licensed in New York and Massachusetts.

Reviewed by:

Daphne Berryhill, RPh

Daphne Berryhill, RPh, has two decades of experience as a clinical pharmacist. She spent most of her career in the Chicago area practicing in-home infusion.

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