Blood Thinner Basics

Medically Reviewed by Melinda Ratini, DO, MS on May 20, 2021

Blood thinners are medicines that help blood flow smoothly through your veins and arteries. They also keep blood clots from forming or getting bigger. They’re used to treat some types of heart disease and heart defects, and other conditions that could raise your risk of getting dangerous clots.

They can protect against heart attacks and strokes. But they also come with risks: For example, they’ll cause you to bleed more than usual when you cut yourself.

The lifesaving benefits of these drugs often outweigh the potential dangers. Still, it's important to learn about both before you start taking them.

Types of Blood Thinners

There are two. The first is called anticoagulants. These keep your blood from clotting, or turning into solid clumps of cells that stick together. Most come in pill form though some such as  heparin, fondaparinux, dalteparin and enoxaparin are given as a shot or as an intravenous infusion. Some of the more widely know anticoagulants include

The second class of blood thinners is called antiplatelets. These target tiny particles in the blood called platelets. They come in pill form, and include:

How They Work

Blood thinners don’t actually make your blood thinner. Nor can they break up clots. But they do keep blood from forming new clots. They can also slow the growth of existing ones.

Some anticoagulants do this by competing with vitamin K from the liver. Your body needs this to make proteins called clotting factors. These help blood cells and platelets (tiny pieces of blood cells) bind together.

Antiplatelets keep platelets from sticking to each other and to the walls of blood vessels. These drugs are weaker than anticoagulants. They’re often prescribed to people at risk for future blood clots, rather than to treat existing ones.

Who Needs Them?

About 2 million to 3 million people take blood thinners every year. You may need them if you’ve already had a heart attack or a stroke, since they can lower your risk of having a second one.

You may also need this type of medicine if you have a heart or blood vessel disease, an irregular heart rhythm, lupus, or deep vein thrombosis. (DVT is a dangerous type of blood clot that often forms in the leg.) You also have a greater risk for blood clots if you’re overweight, recently had surgery, or have an artificial heart valve.

Some people only need these meds for a few months. But if you have ongoing health problems, you may need to take them long term.

If you have atrial fibrillation, blood thinners can help keep you from having a stroke. That’s one of the most common reasons doctors prescribe it.


Clotting isn't always a bad thing: When you cut yourself, it's what seals your wound and keeps you from losing too much blood. Blood thinners prevent clotting. So, even tiny cuts or bruises will bleed a lot more if you take these drugs.

You should be very careful when taking part in activities that could cause any type of injury. Call your doctor right away if you fall or hit your head. Even if you don't tear your skin, you could bleed internally.

Let your doctor know right away if you notice any signs of unusual bleeding, like:

If you take an anticoagulant like warfarin, you'll need regular blood tests so your doctor can adjust your levels if needed. Ask them about other steps you should take to stay safe while you're on this medication. Be careful with activities that can lead to head injuries. Any type of trauma is extremely dangerous if you’re taking a blood thinner.

If you get a dangerous bleeding problem while taking warfarin, doctors can turn to an "antidote" of vitamin K or a combination of prothrombin complex concentrate (PCC) and fresh frozen plasma to stop it. In addition, approval has been given for using a reversal agent like andexanet alfa (Andexxa) to reverse the anti-clotting effects of apixaban (Eliquis) and rivaroxaban (Xarelto) or idarucizumab (Praxbind) to reverse the anti-clotting effects of dabigatran etexilate (Pradaxa). in emergencies.

Other medicines and supplements, including over-the-counter ones, can interfere with these drugs. Tell all of your doctors, including your dentist, that you’re taking a blood thinner. Don’t start any new medicines without their OK.

And remember that your diet is also very important. Some foods -- like green, leafy vegetables -- contain vitamin K. This can counteract the blood thinners. Talk to your doctor about your diet.

Show Sources

SOURCES: American Heart Association: "What Are Anticoagulants and Antiplatelet Agents?" Northwest Primary Care: "Helpful Tips for Those Taking Anticoagulant Medications." Society for Vascular Surgery: "Deep Vein Thrombosis (DVT)." American Academy of Orthopaedic Surgeons: "Deep Vein Thrombosis." UpToDate: "Patient Information: Warfarin (Coumadin)."

© 2021 WebMD, LLC. All rights reserved. View privacy policy and trust info