Warfarin FAQ

Publication Date:
Wed, 07/01/2015
By: Alere Staff

1. What is warfarin?

Warfarin is a class of medication called anticoagulant, a drug that hinders coagulation in the blood. The most common reason a person is put on warfarin is to prevent the development of blood clots in the blood stream.

2. Why is controlling blood clotting so important?

A blood clot is essential to life and forms whenever we experience any type of cut or injury. Because of certain medical conditions, blood clots can form inappropriately, leading to heart attack, stroke, or pulmonary embolism.

Warfarin is often prescribed for people to prevent abnormal clot formation. Some medical conditions include1:

  • Mechanical Heart Valve (MHV)
  • Atrial Fibrillation
  • Venous Thromboembolism or Deep Vein Thrombosis (DVT)
  • Pulmonary Embolism
  • Hypercoagulable state

3. What should I tell my doctor before taking warfarin?

It is always important for you to tell your doctor everything regarding your medical history, including any drinking, smoking or drug use. It is the only way your doctor will be able to best treat you. Most importantly, always tell your doctor of any of the following:

  • Bleeding Problem: This means any bleeding disorders you may have like hemophilia or any stomach or intestinal ulcers you may have had. Also, if you are prone to nose bleeds or, for women, if your periods are particularly heavy.
  • Frequent Falls: Some people do fall frequently for different reasons. If you are one of them, you need to tell your doctor. If you fall and the fall causes you to bleed, it may be more difficult to stop the bleeding while you’re on warfarin.
  • Liver or Kidney Disease: The liver and kidneys are your body’s two main filters. Practically everything you take in, eat or drink goes through your liver and/or kidneys to remove what the body doesn’t need.
  • High Blood Pressure: Whether it is controlled with medication or not.
  • Congestive Heart Failure or Diabetes: Such conditions decrease the body’s ability to circulate blood efficiently.
  • Any other medication you may be taking, including over the counter medication and any herbal supplements or vitamins.
  • If you are following any special diet, especially for weight loss.
  • Future Surgeries or Procedures: These include dental work. Taking warfarin means if you are going to have any procedure or surgery where there is a possibility you will bleed, you need to tell your doctor. They may need to make adjustments to your warfarin doses prior to your procedure to decrease your risk of bleeding.
  • As with any medication, tell your doctor if you are pregnant or plan to become pregnant and whether or not you are breastfeeding.

4. How should I take warfarin?

You should take warfarin EXACTLY as your doctor prescribes it to you.  While you are on warfarin, it will be necessary to check your blood to see if the medication is doing its job. Checking your blood will either require a blood draw or a finger stick to check your INR, a measurement that shows the time it takes for your blood to clot. The test is performed at regular intervals. Medicare allows for weekly testing in line with studies on patient safety.1

  Methods of Blood Testing

  Home INR Monitoring

  • Conducted by patient or caregiver at home
  • Same INR monitors as used in doctor's office
  • Results available in fewer than 2 minutes
  Venous Draw
  • Needle withdrawal by a professional
  • Sent to outside laboratory for analysis
  • Pricing and accuracy varies according to reagent used by lab
  • Patients are called with test results
  Point of Care (POC)
  • Sample taken by finger stick at doctor’s office
  • Testing monitors use most sensitive reagents possible
  • Results available in fewer than 2 minutes
  • Patients learn results without delay

Either way you check your blood, the results of your INR should be within your therapeutic range. If your INR is too high, they may decrease your dose.  If your INR is too low, they may increase your dose.  It is important to follow these adjustments your doctor makes in order to get the best results from your Warfarin therapy.

5. Why do I need to have my blood checked?

Some people on warfarin think their blood is being tested for their “warfarin levels” but this is not true as there is no such test. The component of your blood the doctor is monitoring is known as the International Normalized Ratio, or INR. This is the part of the blood that helps blood clots to form.  Warfarin increases the INR, thereby decreasing the body’s ability to form blood clots. Depending on the instructions given by your prescribing physician, you will need to check your INR at regular intervals to make sure your dose of warfarin is effective. If it is not, the doctor will adjust your dose accordingly.

Always follow your doctor’s instructions on the day you have your INR checked. It is common to take your warfarin AFTER you get your blood drawn or you do your home testing.

6. What should I do if I miss a dose?

It is best not to miss a dose. To remember your dose, take your dose at the same time every day. Using an alarm to alert you to taking your medication can also be helpful. If your doctor suggests you take your warfarin at night, it is helpful to schedule after dinner or before bedtime. If your doctor thinks morning time would be better, schedule it around breakfast, either before or after you eat. If you should miss a dose, call your doctor immediately or follow their instructions if they’ve already been provided beforehand. Typically, if you remember and it’s within 8 hours of when you were supposed to take it, you may take the missed dose. It is not recommended to make up your missed dose and DO NOT DOUBLE YOUR DOSE the next day.

7. What should I avoid while taking Warfarin?

Avoid contact sports or any activity, like mountain biking, which can cause serious injury.

8. What are some of the common side effects of taking warfarin?

Most people on warfarin notice they bruise easier than before they started the medication or it takes longer for their blood to clot if they get cuts. Others experience nose bleeds or small amounts of blood in their urine or stool. Even though these are more common, you should tell your doctor.

Go to the nearest hospital if you experience any of the following:

  • Severe or prolonged nose bleeds
  • Red, dark yellow or cloudy urine
  • Bloody or black, tarry stool
  • Bruising with no cause, meaning you did not hit that part of your body on anything, you didn’t fall, no trauma has occurred
  • Prolonged bleeding from minor cuts
  • Severe or heavier than normal periods
  • Bloody or coffee-ground like vomit
  • Coughing up blood
  • Persistent, severe headaches, backaches (especially upper-mid backache) or stomach pain.

All of these could be a sign/symptom of internal bleeding so, immediate medical attention is very important.

9. Can I take over-the-counter medication, herbal supplements and vitamins while I’m taking warfarin?

In order to avoid drug interactions, it is important to talk with your doctor or pharmacist before starting a new medication, as well as telling your doctor all the medication you are currently taking before starting warfarin, including vitamins and herbal supplements.

Natural Medicines and Vitamins

  • Ginger
  • Iron
  • St. John’s Wort
  • Vitamin A, C, D and E

Over-the-Counter Medications

  • Airborne
  • Aspirin
  • Topical Arthritis Pain Medications

10. Should I follow any special diet?

There is no set diet for someone on warfarin. However, it is important to maintain steady Vitamin K levels in your body. If you have too much Vitamin K in your system, it can decrease the effects of the warfarin and put you at risk for developing a blood clot.  We offer a Vitamin K Finder and articles about diet to assist you. Your doctor can tell you which foods you should limit in your diet or you can ask your doctor to refer you to a nutritionist should you need further guidance.

11. Is it okay to drink alcohol while on warfarin?

Care should be taken when consuming alcohol if you are a warfarin patient. Your physician may have specific instructions based on your condition. For more information on how warfarin and alcohol can interact, check out our article on Alcohol and Warfarin.


  1. CMS Manual Change Pub 100-04 Transmittal 1562 July 25, 2008.
  2. U.S. Food and Drug Administration. Medication Guide: Coumadin (Warfarin Sodium). Retrieved June 17, 2015 from website: http://www.fda.gov/downloads/drugs/drugsafety/ucm088578.pdf
  3. VA Healthcare. Warfarin (Coumadin) FAQ. Retrieved June 17, 2015 from website: http://www.indianapolis.va.gov/docs/warfarin_FAQ_March_2015.pdf