Blood Thinner Pills:

Your Guide to Using 

Them Safely

AHRQ Pub. No. 15-0047-C

Replaces AHRQ Pub. No. 09-0086-C

September 2015
The name of my blood thinner is:

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Reminders:

Call your doctor or pharmacy if you have questions about your 

blood thinner.

My doctor’s contact information is:

My pharmacist’s contact information is:

Notes:

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1

About Your Blood 

Thinner

Your doctor has prescribed a medicine 

called a blood thinner to prevent blood 

clots. Blood clots can put you at risk 

for heart attack, stroke, and other 

serious medical problems. A blood 

thinner is a kind of drug called an 

anticoagulant (an-te-ko-AG-u-lent). 

“Anti” means against and “coagulant” 

means to thicken into a gel or solid. 

Blood thinner drugs work well when 

they are used correctly. To help you learn about your medicine, your doctor 

has given you this booklet to read. 

Warning!

Tell your doctor if you are pregnant 

or plan to get pregnant. Many blood 

thinners can cause birth defects or 

bleeding that may harm your unborn 

child.

Depending on where you receive care, you may be seen by a doctor, nurse, 

physician’s assistant, nurse practitioner, pharmacist, or other health care 

professional. The term “doctor” is used in this booklet to refer to the person 

who helps you manage your blood thinner medicine.

You and your doctor will work together as a team to make sure that taking 

your blood thinner does not stop you from living well and safely. The 

information in this booklet will help you understand why you are taking a 

blood thinner and how to keep yourself healthy. Please take time to read all of 

the information in this booklet.

There are different types of blood thinners. The most common blood thinner 

that doctors prescribe is warfarin (Coumadin®, COU-mad-din). Your doctor 

may also discuss using 

one of the newer blood 

thinners depending on 

your individual situation.
2

How to Take Your Blood Thinner

Always take your blood thinner as directed. For example, some blood 

thinners need to be taken at the same time of day, every day.

Never skip a dose, and never take a double dose. 

If you miss a dose, take it as soon as you remember. If you don’t remember 

until the next day, call your doctor for instructions. If this happens when your 

doctor is not available, skip the missed dose and start again the next day. 

Mark the missed dose in a diary or on a calendar. 

A pillbox with a slot for each day may help you keep track of your medicines.

Check Your Medicine

Check your medicine when you get it from the 

pharmacy. 

■ Does the medicine seem different from 

what your doctor prescribed or look 

different from what you expected? 

■ Does your pill look different from what 

you used before? 

■ Are the color, shape, and markings on 

the pill the same as what you were given 

before? 

If something seems different, ask the pharmacist 

to double check it. Many medication errors are 

found by patients.
3

Using Other Medicines

Tell your doctor about every medicine you 

take. The doctor needs to know about all 

your medicines, including medicines you 

used before you started taking a blood 

thinner. 

Other medicines can change the way your 

blood thinner works. Your blood thinner can 

also change how other medicines work. 

It is very important to talk with your doctor 

about all the medicines you take, including other prescription medicines, 

over-the-counter medicines, vitamins, and herbal products.

Products that contain aspirin may lessen the blood’s ability to form clots and 

may increase your risk of bleeding when you also are taking a blood thinner. 

If you are taking a blood thinner, talk to your doctor before taking any 

medication that has aspirin in it.

Medicines you get over the counter may also interact with your blood thinner. 

Following is a list of some common medicines that you should talk with your 

doctor or pharmacist about before using.

Pain relievers, cold medicines, or stomach remedies, such as:

■ Advil®

■ Aleve®

■ Alka-Seltzer®

■ Excedrin®

■ ex-lax®

■ Midol®

■ Motrin®

■ Nuprin®

■ Pamprin HB®

■ Pepto Bismol®

■ Sine-Off®

■ Tagamet HB®

■ Tylenol®

Vitamins and herbal products, such as:

■ Centrum®, One a Day®, 

or other multivitamins

■ Garlic 

■ Ginkgo biloba

■ Green tea 

Talk to your doctor about every medication and over-the-counter 

product that you take.
4

Talk to Your Other 

Doctors

Because you take a blood thinner, you 

will be seen regularly by the doctor who 

prescribed the medicine. You may also see 

other doctors for different problems. When 

you see other doctors, it is very important 

that you tell them you are taking a blood 

thinner. You should also tell your dentist 

and the person who cleans your teeth.

If you use different pharmacies, make sure each pharmacist knows that you 

take a blood thinner.

Blood thinners can interact with medicines and treatments that other doctors 

might prescribe for you. If another doctor orders a new medicine for you, tell 

the doctor who ordered your blood thinner because dose changes for your 

blood thinner may be needed.

Tell all your doctors about every medication and over-the-counter 

product that you take.

Tell your doctor about all your medicines. 

Always tell your doctor about all the medicines you are taking. 

Tell your doctor when you start taking new medicine, when 

you stop taking a medicine, and if the amount of medicine you 

are taking changes. When you visit your doctor, bring a list of 

current medicines, over-the-counter drugs—such as aspirin—

and any vitamins and herbal products you take. A personal, 

medication wallet card can help you keep track of this list. Go 

to www.ahrq.gov/yourmedicine to download a printable 

wallet card that you can use to record the medicine and other 

products that you take.
5

Possible Side Effects

When taking a blood thinner it is important to be aware of its possible side 

effects. Bleeding is the most common side effect. 

Call your doctor immediately if you have any of the following signs of 

serious bleeding:

■ Menstrual bleeding that is much heavier than normal. 

■ Red or brown urine. 

■ Bowel movements that are red or look like tar. 

■ Bleeding from the gums or nose that does not stop quickly. 

■ Vomit that is brown or bright red. 

■ Anything red in color that you cough up. 

■ Severe pain, such as a headache or stomachache. 

■ Unusual bruising. 

■ A cut that does not stop bleeding. 

■ A serious fall or bump on the head. 

■ Dizziness or weakness. 
6

Stay Safe While Taking 

Your Blood Thinner

Call your doctor and go to the 

hospital immediately if you have had 

a fall or hit your head, even if you 

are not bleeding. You can be bleeding 

but not see any blood. For example, if 

you fall and hit your head, bleeding can 

occur inside your skull. Or, if you hurt 

your arm during a fall and then notice a 

large purple bruise, this means you are 

bleeding under your skin. 

Because you are taking a blood thinner, 

you should try not to hurt yourself and 

cause bleeding. You need to be careful 

when you use knives, scissors, razors, 

or any sharp object that can make you 

bleed. 

You also need to avoid activities and sports that could cause injury. 

Swimming and walking are safe activities. If you would like to start a new 

activity that will increase the amount of exercise you get every day, talk to 

your doctor.

You can still do many things that you 

enjoy. If you like to work in the yard, 

you still can. Just be sure to wear 

sturdy shoes and gloves to protect 

yourself. If you like to ride your 

bike, be sure you wear a helmet. 

Tell others. 

Keep a current list of all the medicines 

you take. Ask your doctor about 

whether you should wear a medical 

alert bracelet or necklace. If you are 

badly injured and unable to speak, the 

bracelet lets health care workers know 

that you are taking a blood thinner.
7

To prevent injury indoors:

■ Be very careful using knives and scissors. 

■ Use an electric razor. 

■ Use a soft toothbrush. 

■ Use waxed dental floss. 

■ Do not use toothpicks. 

■ Wear shoes or non-skid slippers in the house. 

■ Be careful when you trim your toenails. 

■ Do not trim corns or calluses yourself. 

To prevent injury outdoors:

■ Always wear shoes. 

■ Wear gloves when using sharp tools. 

■ Avoid activities and sports that can easily hurt you. 

■ Wear gardening gloves when doing yard work. 
8

Food and Your Blood Thinner

If your doctor has prescribed warfarin, the foods you eat can affect how well 

your blood thinner works for you. High amounts of vitamin K can work 

against warfarin. Other blood thinners are not affected by vitamin K. Ask 

your doctor if your diet can affect how well your blood thinner works. 

For a list of foods that contain vitamin K, go to www.usda.gov and search for 

vitamin K.

If you are taking a blood thinner, you should avoid drinking alcohol.

Call your doctor if you are unable 

to eat for several days, for whatever 

reason. Also call if you have 

stomach problems, vomiting, or 

diarrhea that lasts more than 1 day. 

These problems could affect your 

blood thinner dose.

Keep your diet the same. 

Do not make any major changes in your 

diet or start a weight loss plan unless 

you talk to your doctor first.
9

Blood Tests

You will have to have your blood tested 

often if you are taking warfarin. The blood 

test helps your doctor decide how much 

medicine you need. 

The International Normalized Ratio (INR) 

blood test measures how fast your blood 

clots and lets the doctor know if your dose 

needs to be changed. Testing your blood 

helps your doctor keep you in a safe range. 

If there is too much blood thinner in your 

body, you could bleed too much. 

If there is not enough, you could get a blood clot. 

Regular blood tests are not needed for some of the newer blood thinners.

Important reminders:

■ Take your blood thinner as directed by your doctor.

■ Go for blood tests as directed. 

■ Never skip a dose. 

■ Never take a double dose. 

Too Little Best Range Too Much

May cause a blood clot May cause bleeding
10

This booklet is based on a product developed by Carla Huber, A.R.N.P., M.S., 

Cedar Rapids Community Anticoagulation Clinic, Cedar Rapids, Iowa, under 

AHRQ Grant No. 1 U18 HSO15830-01 to Kirkwood Community College.

This document is in the public domain and may be used and reprinted without 

special permission. Citation of the source is appreciated.

How to Order AHRQ Booklets

For more copies of this booklet, email the AHRQ Publications 

Clearinghouse at AHRQPubs@ahrq.hhs.gov or call the toll-free 

number 1-800-358-9295. 

This booklet and a video on blood thinner pills are available at 

www.ahrq.gov/btpills.htm. For other consumer and patient 

materials, go to the AHRQ Web site at www.ahrq.gov/

consumer.