Blood Thinner Basics

Medically Reviewed by Carmelita Swiner, MD on December 09, 2023
5 min read

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

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

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

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, but some are given as a shot or as an IV through one of your veins. Some of the more widely known anticoagulants include:

  • Apixaban (Eliquis)
  • Dabigatran(Pradaxa)
  • Dalteparin(Fragmin)
  • Edoxaban (Savaysa)
  • Enoxaparin (Lovenox)
  • Fondaparinux(Arixtra)
  • Heparin (Innohep)
  • Rivaroxaban (Xarelto)
  • Warfarin (CoumadinJantoven)

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:

  • Aspirin
  • Cilostazol
  • Clopidogrel (Plavix)
  • Dipyridamole (Persantine)
  • Eptifibatide (Integrilin)
  • Prasugrel (Effient)
  • Ticagrelor (Brilinta)
  • Tirofiban (Aggrastat)
  • Vorapaxar (Zontivity)

Blood thinners don’t actually make your blood thinner. Nor can they break up clots. But they do keep new clots from forming. 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, forming clots. These drugs are weaker than anticoagulants. They’re often prescribed to people at risk for future blood clots, rather than to treat existing ones.

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 blood thinners if you have a heart or blood vessel disease, an irregular heart rhythm, lupus, or deep vein thrombosis (DVT). That’s a dangerous type of blood clot that often forms in the leg. Your risk of getting blood clots is also higher if you’re overweight, you’ve recently had surgery, or you have an artificial heart valve.

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

Clotting isn't always a bad thing. When you cut yourself, that’s what seals your wound and keeps you from losing too much blood. But 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:

  • Heavier-than-normal menstrual periods
  • Blood in your pee or poop
  • Bleeding from your gums or nose
  • Vomiting or coughing up blood
  • Dizziness
  • Weaknesses
  • A severe headache or stomachache

You may lose bone strength if you take heparin for a long time. This raises your chances of breaking a bone. Another serious, but less common, side effect of warfarin is necrosis. That’s when your skin starts to die. 

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. 

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 what you eat is also very important. Some foods – like green, leafy vegetables – contain vitamin K. This can counteract blood thinners. Ask your doctor if you’re not sure a certain food or drink is safe. 

Get your blood checked often if you’re on warfarin or heparin. This is an international normalized ratio (INR) test. It tells you how long it takes your blood to clot.

You can also try to stop uncontrollable bleeding before it starts. Here are a few tips:

  • Use a soft toothbrush and waxed dental floss.
  • Use an electric razor.
  • Don’t trim corns or calluses.
  • Wear gloves when you do yard work or use sharp tools.
  • Wear a helmet when bike riding.
  • Do low-impact sports like walking or swimming.

Other tips include:

Pay attention to how much vitamin K you’re getting. It helps your blood clot. But too much can stop warfarin from working. Talk to your doctor to find the right balance.

Don’t drink too much alcohol. This raises your risk of bleeding. One to two drinks a day is a safe amount.

Tell peopleyou’re on a blood thinner. Wear a medical alert bracelet or carry a card with your medications on it. Make sure your doctor, dentist, and other health care providers know. Tell them if you also take herbal supplements or vitamins.

Call your doctor right away if you have any of these symptoms. You may have a blood clot. They include:

  • Blurred vision
  • Chest pain
  • Severe weakness or dizziness
  • Tingly hands, feet, or face
  • Can’t move
  • Swollen or red arms, calves, or feet

Some are considered safe to take during pregnancy. Others aren’t. Talk to your doctor if you’re on blood thinners and thinking about having a baby. They’ll let you know the next steps. If you’re already pregnant, double check with your doctor to make sure the blood thinner you’re on won’t harm the baby.