Your body needs a healthy flow of blood to get the oxygen and nutrients it needs. Some medical conditions can affect healthy blood flow, putting you at risk of a heart attack or stroke.

To help lower this risk, your doctor might prescribe a medicine that will keep the blood from clotting as easily. These medicines are commonly called blood thinners.

While a blood thinner does not really “thin” your blood, it can lower your risk of a heart attack or stroke by preventing blood clots. If you already have a blood clot, these medicines help to keep it from getting bigger and can help prevent your body from forming new clots.

These medicines can also raise your risk of bleeding, so it is important to know when bleeding or bruising is unusual and when to talk with your doctor.

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What Is a Blood Clot?

If you have a cut or bruise, a blood clot is a good thing. When you damage a blood vessel, small pieces of cells in your blood called platelets stick together to form a clot and send out a signal to draw more platelets to your injury. Once your injury heals, your blood clot usually dissolves on its own.

Clotting is an important function that your body needs to heal itself, but some medical conditions, behaviors, or situations can cause dangerous blood clots to form. This can be life-threatening if a clot moves and blocks blood flow to your brain, heart, or lungs.

When Is a Blood Thinner Used?

Blood thinners are usually prescribed for people who have conditions that affect healthy blood flow, including:

Types of Blood Thinner Medication

There are two main types of blood thinners.


Anticoagulants, like warfarin (or the brand name Coumadin®), slow down the chemical reaction that happens when your blood tries to clot and can also keep clots that have already formed from getting bigger. Some anticoagulants require you to have your blood checked regularly to make sure they are working properly.

Antiplatelet drugs

Antiplatelet drugs like aspirin or clopidogrel (or the brand name Plavix®), keep your platelets from sticking together.

What You Need to Know

Because blood thinners affect your blood’s ability to clot, you might bleed easier than usual. To avoid complications, it is very important to take your medicine exactly how your doctor tells you.

Some other medicines and foods make blood thinners stronger or weaker. Talk to your doctor about all the medicines you take, including over-the-counter drugs, vitamins, and supplements, as well as your diet to make sure that you are not at risk of a bad interaction.

In case of an emergency, carry a card in your wallet that lists all the medicines you take. It’s also a good idea to have a medical alert bracelet showing that you take a blood thinner.

Call your doctor right away if you have any of these symptoms, which may be a sign of major bleeding:

  • Bleeding from your gums or nose that does not stop within a few minutes
  • A wound that does not stop bleeding after you apply pressure to it
  • Blood in your urine or stool
  • Stools that are black like tar
  • Vomiting or coughing up blood
  • Bruises that appear for no reason, get larger or more painful, or are sudden and severe

To learn more about blood thinners, visit the UPMC Heart and Vascular Institute online or call 1-855-UPMC-HVI (876-2484).

About Heart and Vascular Institute

The UPMC Heart and Vascular Institute has long been a leader in cardiovascular care, with a rich history in clinical research and innovation. As one of the first heart transplant centers in the country and as the developer of one of the first heart-assist devices, UPMC has contributed to advancing the field of cardiovascular medicine. We strive to provide the most advanced, cutting-edge care for our patients, treating both common and complex conditions. We also offer services that seek to improve the health of our communities, including heart screenings, free clinics, and heart health education. Find an expert near you.