Warfarin and Supplements: What You Need to Know Before Taking Them Together

When you're on warfarin, a blood thinner used to prevent dangerous clots in people with atrial fibrillation, artificial heart valves, or a history of deep vein thrombosis. Also known as Coumadin, it works by blocking vitamin K, which your body needs to make clotting proteins. But many people don’t realize that everyday supplements, including herbal products, vitamins, and over-the-counter remedies can either make warfarin too strong—or too weak—putting you at risk for stroke or severe bleeding.

Some supplements directly interfere with how warfarin works. Vitamin K, found in leafy greens and multivitamins, is the most common culprit. If you suddenly eat more kale or start taking a vitamin K pill, your INR drops, and your blood clots faster. On the flip side, garlic, fish oil, ginkgo biloba, and ginger can thin your blood even more, increasing your chance of bruising, nosebleeds, or worse. Even St. John’s wort, a popular herb for mood support, speeds up how fast your liver breaks down warfarin, making it less effective. These aren’t just theoretical risks—studies show people on warfarin who take these supplements have hospital visits because their INR went off the charts.

You don’t need to avoid all supplements forever. But you do need to be consistent. If you eat spinach every day, keep eating it. If you take fish oil, stick to the same dose. Sudden changes are the problem. Always tell your doctor or pharmacist about every pill, powder, or tincture you take—even if you think it’s "natural" or "harmless." And never start or stop something without checking first. Your warfarin dose is fine-tuned based on your diet, other meds, and yes, even your supplements. A small change can throw off your balance. The posts below give you real examples of what works, what doesn’t, and what to avoid—so you can stay safe without guessing.