Warfarin Side Effects

As of June 30, 2024, delayed blood clotting, adverse drug interactions, hemorrhaging and gastrointestinal bleeding were the most common warfarin side effects reported to the U.S. Food and Drug Administration. Bruising was also common.

Disclaimer: Reports sent to the FDA don’t necessarily mean the drug caused an adverse event. Consult a health care professional before stopping or changing medication.

Clinical trials showed that between 0.6% and 3% of the study participants had a major bleeding incident. Underlying health conditions and drug interactions may increase this risk. Warfarin products contain a boxed warning about its association with bleeding risks.

Many patients taking warfarin experience gastrointestinal symptoms. These are often manageable with lifestyle changes and over-the-counter medications.

Warfarin can also affect your sense of taste and may contribute to hair loss.

Bleeding is a common side effect of warfarin and other medications that inhibit vitamin K. This is because vitamin K helps your blood clot. Patients may have increased bruising and excessive bleeding from seemingly minor injuries. Doctors can administer vitamin K injections in an emergency to increase clotting.

Warfarin can cause serious side effects such as organ and tissue damage and hemorrhaging. Patients on this medication should monitor themselves for symptoms.

While most of these serious side effects are rare, they may still pose a health risk. You should be aware of the risks and report any serious symptoms to your doctor as soon as possible.

Hemorrhaging is the most common warfarin side effect received through the FDA reporting system. In extreme cases, even a small cut could cause excessive bleeding in patients on warfarin. Without intervention, too much blood loss can be fatal.

Bleeding often occurs when warfarin-containing medications cause an elevated International Normalized Ratio (INR). High INR levels indicate slower-than-normal clotting times.

Certain factors, such as having a history of bleeding disorders, diabetes, kidney problems, high blood pressure or being over the age of 65, can increase the risk of bleeding when taking warfarin.

“Warfarin metabolism can be affected by reduced renal function and hepatic function, which is more prevalent in older patients,” clinical pharmacist Kenneth S. Fill told Drugwatch.

“Additionally, patients with bleeding disorders can be at an increased risk of complications from warfarin such as tissue necrosis or calciphylaxis, which requires extra monitoring.”

Some common painkillers, including aspirin, ibuprofen and naproxen, can also increase your bleeding risk – especially if taken with warfarin.

In 2006, the FDA issued a boxed warning for the increased risk of bleeding among patients taking warfarin. It recommends routine testing of INR levels and patient education.

Tissue death is a rare complication that may start within a few days of beginning warfarin therapy. Improper blood supply causes tissue death, which can lead to gangrene and breakdown.

Symptoms of warfarin-induced necrosis often begin with a painful red discoloration on the skin. This may progress to a blue or black discoloration. Typically, this symptom develops on the thighs, breasts, penis or buttocks. These patches eventually develop large bloody blisters. If left untreated, necrosis can affect internal organs and lead to death.

Another cause of warfarin-associated necrosis is calciphylaxis. This is a condition where calcium deposits block arteries. Painful red or purple web-like patterns on the skin are among the earliest symptoms of calcium buildup. These purplish lesions often appear on the legs and look similar to skin necrosis lesions.

According to a 2023 case study published in Practical Dermatology, survival rates for necrosis caused by warfarin-induced calciphylaxis range from 48% to 78%.

Managing Side Effects

While you may not be able to remove all risks of taking warfarin, you can reduce your chances of having a serious adverse reaction.

Do not take warfarin with other pain relievers unless specifically instructed by your doctor, as they may increase your bleeding risk.

Your doctor should carefully monitor blood levels to help ensure your safety while taking warfarin. Patients on warfarin must undergo INR tests monthly to determine how quickly their blood clots.

Alternatives to warfarin became widely available in the 2010s. Some doctors now favor newer medication classes that don’t inhibit vitamin K.

However, warfarin is still the preferred blood thinner for some patients.

Warfarin is a vitamin K antagonist that blocks the body’s ability to synthesize Vitamin K for blood clotting purposes.

Newer blood thinner classes, such as direct oral anticoagulants, work by blocking the proteins involved in binding blood cells together. These drugs are also called factor Xa inhibitors.

“Compared to warfarin, the new anticoagulants have a more predictable dose response, making them less of a bleeding risk,” Fill said. “These newer medications also generally interact with less medications compared to warfarin.”

While direct oral anticoagulants are often better tolerated compared to warfarin, they still pose an increased risk of bleeding.

You should discuss your concerns about side effects with a health care provider to see if warfarin or DOACs are a better choice for your treatment.

Editor Lindsay Donaldson contributed to this article.