Warfarin Interactions: What Drugs and Supplements Can Be Dangerous With It
When you take warfarin, a blood thinner used to prevent dangerous clots. Also known as Coumadin, it's one of the most common anticoagulants prescribed worldwide — but it doesn't play nice with many other substances. Even small changes in your diet, other meds, or supplements can throw off your INR levels and put you at risk for bleeding or clots. This isn't theoretical — people end up in the ER every day because they didn't realize their new antibiotic or herbal pill was messing with warfarin.
One of the biggest players in warfarin interactions is vitamin K, a nutrient that helps your blood clot. If you suddenly eat a lot of kale, spinach, or broccoli — all high in vitamin K — your warfarin becomes less effective. On the flip side, if you stop eating those foods cold turkey, your INR can spike dangerously high. It’s not about avoiding them entirely — it’s about keeping your intake steady. Then there’s CYP2C9 enzyme, the liver system that breaks down warfarin. Anything that slows it down — like some antibiotics, antifungals, or even grapefruit juice — can cause warfarin to build up in your system. That’s when bruising, nosebleeds, or worse can happen.
Some common medications people don’t realize are risky include amiodarone, a heart rhythm drug, and fluconazole, a fungal infection treatment. Even over-the-counter painkillers like ibuprofen or naproxen can increase bleeding risk when taken with warfarin. And don’t forget supplements — garlic, ginkgo, ginseng, and fish oil all thin the blood on their own and can multiply warfarin’s effects. Your doctor doesn’t always ask about these, so you have to speak up.
What you’ll find in the posts below are real, practical stories and science-backed facts about how warfarin interacts with other drugs, supplements, and even your daily habits. You’ll see how people managed these risks, what labs to track, and which combinations are absolute no-gos. No fluff. No guesswork. Just what you need to stay safe while taking this powerful medication.
