Warfarin Side Effects: What You Need to Know About Bleeding, Diet, and Safety

When you're taking 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's one of the most prescribed anticoagulants in Canada—but it demands careful handling. Warfarin doesn’t just thin your blood; it changes how your body responds to food, other medicines, and even minor injuries. That’s why knowing its side effects isn’t optional—it’s life-saving.

The biggest risk with warfarin is bleeding, uncontrolled or unexpected hemorrhaging. It can show up as nosebleeds that won’t stop, gums bleeding when you brush, purple spots under your skin, or blood in your urine or stool. In rare cases, it leads to internal bleeding in the brain—symptoms like sudden headaches, dizziness, or confusion need emergency care. But bleeding isn’t random. It’s tied directly to your INR, a blood test that measures how long it takes your blood to clot. If your INR is too high, you’re at risk. Too low, and clots can still form. That’s why regular blood tests aren’t just routine—they’re your safety net.

What you eat matters more than you think. vitamin K, a nutrient found in leafy greens like spinach, kale, and broccoli directly fights warfarin’s effect. You don’t need to avoid these foods—just keep your intake consistent. Eating a big salad one day and none the next can make your INR swing wildly. Same goes for alcohol, cranberry juice, and certain herbal supplements like St. John’s wort or ginkgo biloba. These aren’t just "maybe" risks—they’re well-documented triggers for dangerous interactions.

Many people on warfarin also take other meds—antibiotics, painkillers, even over-the-counter cold remedies. Some of these can boost warfarin’s effect without you knowing. That’s why your pharmacist is your best friend here. Always tell them you’re on warfarin before picking up anything new. And never skip your INR checks. Even if you feel fine, your numbers can drift.

Warfarin isn’t going away. It’s cheap, effective, and backed by decades of use. But it’s not a set-it-and-forget-it drug. Managing it means staying alert to your body, your diet, and your meds. The side effects are real—but so are the tools to control them. Below, you’ll find real-world advice on how to stabilize your INR, avoid dangerous interactions, and live safely with warfarin. No fluff. Just what works.