Warfarin and COVID-19: What You Need to Know About Blood Thinners During the Pandemic

When you're on warfarin, a blood thinner used to prevent dangerous clots in people with atrial fibrillation, deep vein thrombosis, or artificial heart valves. Also known as Coumadin, it works by slowing down your body's clotting process. But when COVID-19 hits, that balance can shift—fast. The virus triggers abnormal clotting in some patients, even those who are otherwise healthy. For people already taking warfarin, this means your INR levels—the measure of how long it takes your blood to clot—can become unpredictable. A spike could mean bleeding risk. A drop could mean a clot forming when you least expect it.

This isn't theoretical. Studies from 2020 to 2023 showed that patients on warfarin who got COVID-19 had higher rates of INR fluctuations than those without the infection. Why? The virus causes inflammation, changes liver function, and can mess with how your body breaks down warfarin. Some people need higher doses. Others need less. And it doesn't always show up right away. That’s why regular INR checks became critical during the pandemic—even more than before. If you're on warfarin and get sick with COVID-19, don't wait for symptoms like unusual bruising or swelling. Call your doctor. Get your INR tested. Don’t assume your usual dose still works.

It’s not just about the drug itself. anticoagulants, medications that prevent blood clots by interfering with the clotting cascade like warfarin interact with so many things: antibiotics, herbal supplements, even changes in your diet. During COVID-19, people often eat less, lose their appetite, or take new OTC meds for fever or congestion. All of that can throw off your INR. INR monitoring, the standard test to measure how well warfarin is working by checking how long blood takes to clot isn’t optional here. It’s your safety net. If you can’t get to a lab, ask about home testing kits—many insurers covered them during the pandemic for good reason.

And while some patients were switched to newer blood thinners like apixaban or rivaroxaban during COVID-19, that’s not always possible. Warfarin is still widely used because it’s cheap, well-studied, and reversible if bleeding happens. But that means you need to be extra careful. No guessing. No skipping tests. No ignoring symptoms like shortness of breath, chest pain, or sudden leg swelling—those could mean a clot, not just a lingering cough.

What you’ll find below are real, practical guides from people who’ve been there. From how to track your INR at home to what foods to watch out for when you’re sick, from when to call your doctor after a positive test to how to avoid dangerous drug interactions with common cold meds—these posts give you the tools to stay safe without panic. You don’t need to understand every detail of coagulation pathways. You just need to know what to do next.