Blood Thinner Basics

Medically Reviewed by Zilpah Sheikh, MD on June 05, 2024
9 min read

Blood thinners are medicines that help your blood flow smoothly through your veins and arteries. They keep blood clots from forming or getting bigger. Blood clots can increase your risk of having a heart attack, stroke, or getting other kinds of heart disease. Your doctor may prescribe a blood thinner to help prevent heart attacks and strokes if you are at risk.

Like all medicines, blood thinners have some 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 types of blood thinners: anticoagulants and antiplatelets.

Anticoagulant blood thinners

Anticoagulants slow down how fast your blood clots and keeps any clots that do form from getting bigger. Most anticoagulants 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 are:

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

Antiplatelet blood thinners

Antiplatelets help keep your blood from forming clots by keeping proteins in your blood (platelets) from sticking together. These can come as pills, suppository, and IV form. Some examples of oral antiplatelets include:

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

Your body makes blood clots from red blood cells, platelets, fibrin, and white blood cells. Anticoagulants and antiplatelets keep these parts from sticking together and forming new clots. They also slow the growth of existing clots.


These work by preventing or undoing coagulation, which is how your body starts to make clots. Different anticoagulants work at different parts of the coagulation process. For instance, some anticoagulants do this by competing with vitamin K, which your body needs to make proteins called clotting factors. These help your blood cells bind together to make blood clots. 


These work by blocking a protein that makes your platelets stick together and to the walls of your blood vessels, forming clots. Different antiplatelets block different proteins in this process. They’re often prescribed to people at risk of having future blood clots, rather than to treat existing ones.

Anticoagulants are some of the most commonly prescribed medicines. You may need an anticoagulant if you have:

Atrial fibrillation. This is an irregular heartbeat that starts in the upper chambers of your heart. This can cause your blood to pool, which makes blood clots more likely. Anticoagulants can help keep your blood from pooling and clotting.

Heart valve surgery or replacement. Some procedures can raise your risk of getting a blood clot where your new valve was placed. Anticoagulants help keep these clots from forming.

Hip or knee replacement. You may have a higher chance of getting clots in the veins in your legs after a hip or knee replacement. This is called deep vein thrombosis, which can cause a pulmonary embolism, which is when a blood clot breaks off your blood vessel and travels to your lungs, where it gets stuck. This can be life-threatening. But anticoagulants can help prevent deep vein thrombosis after surgery.

Blood clotting disorders. Some people are born with a condition where their blood clots more easily than in other people. Anticoagulants can help prevent them from having complications, such as deep vein thrombosis, due to their condition.

You may need an antiplatelet if you are at risk of having a heart attack or stroke because you have:

  • Angina (chest pain that comes and goes)
  • Atrial fibrillation
  • Coronary artery disease
  • Had a heart attack
  • Peripheral vascular disease (clogs in veins and arteries not in your heart)
  • Surgery on your heart, such as placement of a stent or heart valve surgery


Atrial fibrillation is one of the most common heart rhythm problems. If you don't treat it, you are at a higher risk of having a stroke.

Your doctor will manage your atrial fibrillation in a few ways by prescribing medicine to:

  • Control your heart rate
  • Make your heart rhythm regular
  • Reduce your risk of having a stroke

If you have atrial fibrillation, your doctor may prescribe blood thinners (especially anticoagulant medicines) as part of your treatment plan. These will help reduce your risk of having a stroke.

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 you're taking blood thinners and doing things 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.

Possible side effects of blood thinners in older adults

If you are over 65 years old, you're more likely to have more than one medical condition that you take medicine for. Some foods and medicines can change the way your blood thinners work, especially if you take warfarin. Make sure your doctor knows all the medicines and supplements you take so they can help make sure you don't have interactions.

Your side effects may include:

  • Back or chest pain
  • Bowel or bladder dysfunction
  • Easy bruising
  • Blood in your pee or poop
  • Black or dark-colored poop
  • Uncontrollable bleeding

Get your blood checked often if you’re on warfarin or heparin. Your doctor will test you with an international normalized ratio (INR) test. This 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. Vitamin K 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 all your doctors that you take 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.

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 or supplements without talking to your doctor first.

Take extra caution while you do any daily tasks that could increase your chance of bleeding. For instance:

  • Be careful when you use knives or scissors.
  • Use an electric razor to shave.
  • Use a soft toothbrush and waxed dental floss to keep your gums from bleeding.
  • Don't use toothpicks.
  • Be careful when you cut your nails.
  • Wear shoes and slippers while inside to keep from getting a foot injury.
  • Wear gloves when gardening or using outdoor tools.

What to avoid when taking blood thinners

Here are a few things you shouldn't do while you're on blood thinners:

Playing risky sports, such as hockey, soccer, football, skiing, gymnastics, or ice skating. These activities increase your chance of getting an injury that causes you to bleed.

Eating foods with too much vitamin K. Such foods include:

  • Greens, such as collard, turnip, spinach, and kale
  • Broccoli
  • Roasted cashews
  • Roasted soybeans and edamame

Consuming juice and whole fruit from cranberries, grapefruit, and pomegranates

Drinking too much alcohol, which can affect how your blood clots and increase your chance of falling

Taking herbal supplements, such as gingko biloba, garlic, melatonin, turmeric, peppermint oil, and St. John's Wort

Using over-the-counter pain relievers, such as aspirin, ibuprofen, naproxen sodium, Alka-Seltzer, acetaminophen, Excedrin, or certain medicines for fungal infections

Having a tooth pulled or dental implants placed

Alcohol is itself a blood thinner, and it also increases the time your blood thinner medication stays in your system. For these reasons, drinking alcohol while taking blood thinners can make it hard for your blood to clot, which can increase your risk of bleeding heavily.

It's best to avoid alcohol while you are taking blood thinners. But if you do drink, don't have more than one to two drinks at a time.

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.

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

If your doctor has prescribed you a blood thinner, it's important that you take your medicine as prescribed. Natural blood thinners aren't a substitute for your medicine.

But you may be able to prevent blood clots in the first place by eating a healthy diet including foods with vitamin K.

How can I thin my blood naturally?

An easy and healthy way to keep your blood flowing smoothly is to eat foods with a high level of vitamin K. Some foods highest in vitamin K are:

  • Fermented soy (natto), soybeans (edamame), and soybean oil 
  • Greens like collard, turnip, spinach, and kale
  • Cooked broccoli
  • Canned pumpkin
  • Carrot juice
  • Raw okra
  • Pine nuts
  • Blueberries
  • Pomegranate juice
  • Roasted chicken breast
  • Grapes
  • Canola oil
  • Olive oil

You can help your body absorb vitamin K by eating a bit of healthy fat when you eat these foods. Healthy fats include avocados, olive or avocado oil, nuts or nut butters, whole or 2% milk and yogurt, olives, and seeds.

Some herbs may also help keep your blood thin. Before you start taking any new supplement, make sure you talk to your doctor, especially if you're taking medicine. Many supplements can interfere with your medicine. Some herbs and supplements that have anticoagulant and/or antiplatelet effects include:

  • Aloe
  • Cranberries
  • Feverfew
  • Garlic
  • Ginger
  • Gingko biloba
  • Meadowsweet
  • Turmeric
  • White willow
  • Chamomile
  • Fenugreek
  • Red clover
  • Dong quai
  • Evening primrose
  • Ginseng

What fruits are natural blood thinners?

Some fruits that have blood-thinning effects are:

  • Pumpkin (canned)
  • Blueberries
  • Pomegranates
  • Grapes
  • Cranberries

Blood thinners are medicines that help keep you from forming blood clots as easily, which keeps your blood flowing smoothly through your veins and arteries. This can help reduce your risk of having a heart attack or stroke if you're at risk. Since blood thinners make you less able to form clots, if you're taking them, be extra careful when you do anything that could increase your chance of injury and bleeding.

Is Tylenol a blood thinner?

No, acetaminophen (Tylenol) is not a blood thinner. It's generally safe to take acetaminophen while you're on a blood thinner, but make sure you follow the directions. Acetaminophen can cause liver damage if you take more than the recommended dose.