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, even small changes in your diet or supplements can throw off your treatment. Warfarin works by blocking vitamin K, which your body needs to make clotting factors. But many herbal supplements, natural products people take for energy, sleep, or inflammation also affect vitamin K levels or how your liver processes warfarin. This can cause your INR—your blood’s clotting time—to spike dangerously high or drop too low, leading to bleeding or clots.
Some herbs are known to interact with warfarin in clear, dangerous ways. Ginseng, often used for stamina and immune support can make warfarin less effective, raising your risk of stroke. St. John’s Wort, a popular mood support herb speeds up how fast your body breaks down warfarin, meaning you might not get enough protection from clots. Then there’s garlic, famous for heart health, which can thin your blood even more—adding to warfarin’s effect and increasing bleeding risk during surgery or injury. Even common supplements like vitamin K, the very nutrient warfarin fights against, can undo your treatment if you suddenly eat a lot of kale, spinach, or take a daily pill. Your INR doesn’t just depend on your warfarin dose—it’s a balancing act with everything you put in your body.
You don’t have to give up all supplements, but you need to know what’s safe. If you’ve been taking ginger for nausea, turmeric for joint pain, or green tea for weight loss, talk to your doctor or pharmacist before continuing. These aren’t harmless teas—they’re active ingredients that change how your blood behaves. Many people assume "natural" means "safe," but that’s not true with warfarin. A study in the Journal of Thrombosis and Haemostasis found that over 40% of patients on warfarin used herbal products, and nearly half of them had unexplained INR swings linked to those supplements. Your care team needs to know everything you’re taking—not just prescriptions. That’s why asking your pharmacist about herb interactions isn’t optional—it’s lifesaving. Below, you’ll find real cases and clear guidance on what to avoid, what to monitor, and how to keep your warfarin working the way it should.
Dong Quai and warfarin can dangerously increase bleeding risk when taken together. Learn why this herbal supplement is not safe for people on blood thinners, what the evidence shows, and what to do instead.
