When you’re on warfarin, a blood thinner used to prevent dangerous clots in people with atrial fibrillation, artificial heart valves, or deep vein thrombosis. Also known as Coumadin, it works by blocking vitamin K’s role in clotting. But warfarin doesn’t work in a vacuum. What you eat directly changes how well it works — and that’s where the warfarin diet, a set of eating guidelines to keep your INR steady and avoid bleeding or clotting risks comes in.
The biggest player in this game is vitamin K, a nutrient your body needs to make clotting factors, which warfarin tries to suppress. Leafy greens like spinach, kale, and broccoli are packed with it. That doesn’t mean you have to quit them. It means you need to keep your intake consistent. If you eat a big salad every day, your INR stays stable. But if you go from no greens to three big servings a day, your INR can drop — and your risk of clotting goes up. The same goes for green tea. One cup? Usually fine. Matcha daily? That’s a different story — it’s concentrated, and it can push your INR too low.
It’s not just greens. Some supplements like ashwagandha, often taken for stress or sleep, can interfere with warfarin indirectly by affecting liver enzymes. Alcohol? It can spike your INR and raise bleeding risk, especially if you drink heavily or binge. Even cranberry juice, often thought to be harmless, has been linked to dangerous INR spikes in some people. And don’t assume that because something is "natural," it’s safe — many herbs and supplements act like drugs in your body.
What you need isn’t a rigid list of forbidden foods. It’s consistency. Your doctor or pharmacist checks your INR levels, a blood test that measures how long it takes your blood to clot, with a target range usually between 2.0 and 3.0 for most people on warfarin. If your INR is too high, you risk bleeding. Too low, and clots form. Your diet is one of the top three reasons (along with other meds and illness) that your INR drifts. That’s why the best advice isn’t "avoid vitamin K" — it’s "eat the same amount every week."
Some people think they need to cut out all green vegetables. That’s wrong. You can still have broccoli, Brussels sprouts, and even kale — just don’t suddenly start eating them every day if you didn’t before. Keep your portions steady. Use the same measuring cup for your salads. Stick to your usual spinach smoothie routine. That’s how you keep your INR where it needs to be.
And if you’re switching to a new generic version of warfarin? Watch out. Even small changes in the formulation can affect how your body absorbs it. That’s why some people need dose adjustments after a switch — not because the drug changed, but because their body now processes it differently. That’s why you need to check your INR after any change — medication, diet, or even a new supplement.
Below, you’ll find real, practical posts that break down exactly how green tea, vitamin K, and other common foods and supplements interact with warfarin. You’ll learn what to track, what to avoid, and how to talk to your doctor without sounding confused. No fluff. Just what works — based on what people actually experience.
