INR Spikes: What Causes Them and How to Stay Safe

When your INR spikes, a measure of how long it takes your blood to clot. Also known as international normalized ratio, it's a critical number for people taking warfarin, a blood thinner used to prevent dangerous clots. If your INR goes too high, you risk serious bleeding—even from a minor bump. If it drops too low, clots can form and trigger strokes or heart attacks. Keeping it steady isn’t about luck—it’s about understanding what changes it.

Vitamin K, a nutrient found in leafy greens and some oils, directly fights warfarin’s effect. Eating a big bowl of kale one day and skipping it the next can send your INR swinging. It’s not that you need to avoid these foods—it’s that you need to eat them consistently. Same goes for alcohol, antibiotics, and even some herbal supplements like garlic or ginseng. These don’t just "interfere"—they actively change how warfarin works in your body. Many people don’t realize that a simple change in their daily routine, like switching brands of ibuprofen or starting a new multivitamin, can trigger an INR spike weeks later.

Some drug interactions are silent killers. For example, taking antibiotics, commonly prescribed for infections while on warfarin can cause your INR to rise suddenly, even if you’ve been stable for months. The same goes for certain antifungals, SSRIs, and even some OTC cold meds. It’s not just about what you take—it’s about when you take it, how much you take, and whether your doctor knows about every pill, powder, or drop you’re using. That’s why regular INR checks aren’t optional—they’re your early warning system.

You don’t need to live in fear, but you do need to be aware. INR spikes don’t happen out of nowhere. They’re the result of small, often overlooked changes in diet, medication, or health. The good news? Once you know the triggers, you can control them. The posts below cover real cases, practical tips, and science-backed strategies to keep your INR steady—from managing vitamin K intake to spotting hidden drug interactions that could put you at risk. You’ll find clear guidance on what to eat, what to avoid, and how to talk to your pharmacist about potential risks before they become emergencies.