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  • Gregg M. Yamada, MD FACC

Warfarin: What You Must Know. What You Must Do.

Warfarin Use: Tips and Precautions
  • Warfarin (also called coumadin) is an important blood thinner. It is not aspirin.

  • Warfarin is much stronger than aspirin and works differently.

Your cardiologist has prescribed warfarin because you have a mechanical valve, pulmonary embolus, DVT or atrial fibrillation (unable to utilize newer medications such as Eliquis, Xarelto, Pradaxa). These conditions require your blood to be thinned to avoid clots which may lead to death, stroke, loss of limb or organ function.

Warfarin use is serious business, so please take it seriously! There is a rare patient who ‘does not care’ to follow instructions. This will lead to the patient being discharged from the medical practice for noncompliance and/or potentially suffering a serious warfarin-related complication.

Excellent Resources You Must Read:

I advise all patients to take the time to do their own reading. Avoid one-way conversations with your physician. Be an active participant in your health care. Be prepared to ask questions.

  • Here are three excellent sources of information that I have organized for you:

  1. The American Heart Association: Warfarin. Click here.

  2. Cleveland Clinic: Warfarin: what you need to know. Click here.

  3. Mayo Clinic: Warfarin. Click here.

Additional Tips and Precautions:

  • Never take new medications, prescription or over the counter, or online supplements unless you first check with the doctor prescribing your warfarin. Warfarin has many interactions with foods and medications.

  • Never take warfarin incorrectly: Don’t miss dosages; take warfarin at different times; draw your INR at different times. Be consistent.

  • Never take aspirin or NSAIDS: no Motrin, Advil, Celebrex, Naprosyn, etc. (Note: there are situations in which your cardiologists WILL prescribe aspirin and/or other blood thinners with warfarin and your cardiologist will discuss with you. The information presented here is meant to give you background on blood thinners)

  • Never draw your INR on Friday (unless we advise you), Saturday, Sunday or holidays.


Warfarin is vitamin K dependent. The newer anticoagulants known as DOACs (Xarelto, Eliquis, Pradaxa) are not dependent upon vitamin K. If you are prescribed Eliquis, for example, you do not have to limit green vegetables or other vitamin K containing foods.

  • Eat approximately the same amount of Vitamin K containing foods every day. Imagine that you have a large bag of all the vegetables you will eat for an entire week. Think of separating these greens into 7 ziploc bags so that you eat the same amount and type of vegetables and fruits daily.

  • The best way to maintain your proper INR is to eat a consistent diet with similar foods. Sounds boring, but if your INR is out of line, you will end up having blood draws every week.

Download the American Heart Association PDF that outlines foods high and low in Vitamin K. Click here.

Summary of Warfarin Use for Atrial Fibrillation in My Practice for My Patients:

(Your Cardiologist's Practice Will DIffer. Other Cardiac Conditions May Have Different Goals of Therapy)

  • What is the lab goal? INR goal 2-3

  • What is the best time to take warfarin? 5 pm: before or after dinner

  • What time of day should I draw my INR? Draw your INR at nearly the same time each month, as early in the day as possible. E.g. no later than 800 am.

  • Will your office call me with results? Yes. Be sure to have your cell phone on and answer it when the office calls you.

  • What if your office calls and leaves instructions on my voicemail? If you receive instructions by voicemail, follow them, but also call our office back to acknowledge you received the instructions.

  • What if your office does not call? Then, call my office at find out why. There may be a problem with the lab draw.

  • What if another doctor orders an INR to be included with a lab test, but you don’t know about it? This happens on occasion and it is a real problem. You must call my office to inform us that another doctor ordered your INR.

For My Patients, Notify My Office If You Have:

  • Changed your diet: eating more or less vitamin K containing foods. Do not start programs such as intermittent fasting without our knowledge.

  • Been prescribed a new medication: any medication such as antibiotics, prednisone, medications for arthritis.

  • Have taken supplements that you bought over the counter or online. You must not take any supplements without first notifying my office.

  • Accidentally missed more than two doses. If you miss one dose, do not take two doses, but simply take the prescribed dose the next day.

  • Notice any unusual bleeding or bruising.

  • Have any questions about warfarin use.

Note: Understanding your heart condition is not difficult. Patients become frustrated and confused when doctors don’t explain things clearly. If you don’t understand what your doctor is talking about, then you won’t be able to ask meaningful questions. I hope that my posts provide you with a framework that you can build upon to become an active participant in your healthcare.

Stay Healthy!

Gregg Yamada MD FACC


Disclaimer: I hope you find my medical blogs to be pertinent, interesting, thought provoking, and even humorous. The information provided is educational and should not be taken as medical advice. I am a doctor, but I am not your doctor. Please schedule an appointment with your doctor to discuss these issues and to determine what is right for you.

© 2020. Gregg M. Yamada, MD FACC. All rights reserved.

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