Blood Thinners: Anticoagulants & Antiplatelet Drugs

Blood thinners have been around since the mid-1900s. Although the name is misleading — they do not actually “thin” the blood — they effectively prevent blood clots from forming in patients at high risk for diseases of the heart and blood vessels. Blood thinners can lead to serious, potentially life-threatening bleeding.

Last Modified: July 28, 2022
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warfarin pills

Doctors often prescribe blood thinners to people with existing health conditions that affect the heart and blood vessels, as well as those who are at a greater risk for such conditions. Blood thinners can also be prescribed after some surgeries, such as hip or knee replacement surgery.

Blood thinners can prevent clotting and stave off growth of existing clots, but they are not without risks. Bleeding is the primary risk associated with blood thinners. This potential side effect can be mild or serious, ranging from bruising to hemorrhagic stroke, bleeding in the brain that requires emergency care.

Patients taking blood thinners should always defer to their doctors about the risks and benefits of the prescribed medication. It is also wise to take blood thinners exactly as prescribed to avoid any unnecessary risks or side effects.

What Are Blood Thinners?

Blood thinners are medications used to prevent blood clots from forming. They can also keep existing clots from getting larger and blocking more blood flow through the body’s vessels. These medications, when used correctly, prevent blood clots, heart attacks, strokes, and other heart- and blood vessel-related complications.

The two main types of blood thinners are anticoagulants, which include warfarin and heparin, and antiplatelet drugs, such as aspirin.

Common blood thinner medications include:
  • Pradaxa (dabigatran)
  • Eliquis (apixaban)
  • Xarelto (rivaroxaban)
  • Coumadin (warfarin)
  • Aspirin
  • Plavix (clopidogrel)
  • Effient (prasugrel)
  • Brilinta (ticagrelor)
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When Are Blood Thinners Prescribed?

Blood thinners are prescribed to treat a variety of health conditions that can cause blood clots.

Clots that form in the arteries, veins and heart can lead to heart attacks, strokes and blockages that can cause other health problems.

Signs and symptoms of blood clots in the arms and legs include swelling, warm sensations, inflammation or redness, pain or tenderness, and skin discoloration on the surface of the skin of the affected area.

Symptoms may vary or become worse when the clot forms deeper in the veins, a condition known as deep vein thrombosis (DVT) or travels to the lungs, resulting in a pulmonary embolism (PE). If the clot affects other parts of the body, such as the heart, kidneys or brain, symptoms can include chest pain, shortness of breath, headaches, and dizziness.

Atrial fibrillation (AFib) is a type of irregular heartbeat that is often treated with blood thinners. People with this condition are five times more likely than those without AFib to suffer from a stroke. Patients with AFib who have a stroke are also more likely to experience permanent disability.

Your doctor may prescribe a blood thinner if you have any of the following conditions:
  • Heart disease
  • Atrial fibrillation
  • Diseases of the blood vessels, such as DVT or PE
  • Heart valve replacement
  • Congenital heart defects
  • Post-surgery when there’s a risk of blood clots
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IVC Filter Information
People who are at risk of deep vein thrombosis or pulmonary embolism are candidates for IVC filters, a small metal device designed to prevent blood clots from entering the heart and lungs.
Learn More

How Do They Work?

Blood thinners do not actually “thin” the blood. Instead, they help blood flow smoothly through blood vessels and work to reduce a person’s risk of forming blood clots.

Blood thinners do not dissolve or break up existing clots. But they can prevent existing clots from getting larger.

Illustration of how vitamin k helps form blood clots.

Blood thinners work in different ways. Some act by blocking or weakening vitamin K and its blood clotting effects. Others block proteins or enzymes that bind blood cells and platelets.

One type of blood thinner also works to keep platelets from sticking together or to the walls of blood vessels.

Types of Blood Thinners

There are a variety of blood thinners, both new and old, that fall under two categories. The first group of blood thinner medications is called anticoagulants. “Anti” means against and “coagulant” means to thicken into a gel or solid. Coagulation is the process of blood clotting.

Warfarin pill.
Warfarin is an anticoagulant blood thinner.

Warfarin is an anticoagulant blood thinner that has been around since the 1950s. Despite the fact that newer blood thinners are now on the market, the U.S. Food and Drug Administration has estimated that approximately two million people still take warfarin.

But even with the continued popularity of this tried-and-true anticoagulant, a newer class of blood thinners has been introduced in recent years. Pradaxa, Xarelto, Eliquis and Savaysa are among the blood thinners approved by the FDA since 2010.


Anticoagulants slow the body’s process of making clots by targeting clotting factors — proteins thrombin and fibrin — and vitamin K.

Types of Anticoagulant Drugs
Heparin is a fast-acting liquid medication administered by injection. It prevents the blood-clotting proteins thrombin and fibrin from working to form clots.
Lovenox (enoxaparin)
This injectable blood thinner is also made from heparin but produces a more predictable anticoagulant response. This means it does not require the close monitoring needed with heparin. Patients can therefore administer the medication at home themselves.
Pradaxa (dabigatran)
Pradaxa, which hit the market in 2010, belongs to a newer class of blood thinners. Taken by mouth, the anticoagulant works by inhibiting the clotting effects of the enzyme thrombin.
Eliquis (apixaban)
Approved in 2012, this blood thinner belongs to the same class of oral medications as Pradaxa. Eliquis acts on an enzyme — Factor Xa — that plays a role in the production of thrombin.
Xarelto (rivaroxaban) and Savaysa (edoxaban)
Xarelto was approved in 2011 and Savaysa in 2015. Both of these medicines also block Xa.
Coumadin (warfarin)
Coumadin is the oldest of the blood thinners. Warfarin’s discovery began in the early 1920s with mysterious hemorrhaging cattle and ended with the development of an anticoagulant medicine that blocks the formation of vitamin K-dependent clotting factors. Its antidote is vitamin K.
Elmiron Information
Elmiron, or pentosan polysulfate sodium, is a weak anticoagulant. This means it works like a blood thinner and makes it harder for blood to clot.
Learn More

Antiplatelet Drugs

Antiplatelet drugs make up the second group of blood thinners. Platelets — also called thrombocytes — are a component of the blood that stops bleeding by clumping together at the site of blood vessel injuries.

Antiplatelet drugs prevent platelets from clumping together to form a clot. Many of these medications act on receptors, proteins that receive chemical signals and cause cells to bind, to achieve this effect.

Antiplatelet medications are not often prescribed to patients with existing blood clots. Instead, they may be used to treat individuals who are at risk of blood clot formation.

Types of Antiplatelet Drugs
Plavix (clopidogrel)
This antiplatelet drug works by binding to P2Y12 ADP platelet receptors, thereby limiting the ability of platelets to clump together. Its effects are irreversible.
Effient (prasugrel)
This medication also works by binding to P2Y12 ADP platelet receptors and limiting platelets' ability to clump together. Its effects are irreversible.
Brilinta (ticagrelor)
This antiplatelet drug interacts with the P2Y12 ADP receptor to keep platelets from sticking together. Its effects, unlike those of Plavix and Effient, are reversible.
Persantine (dipyridamole)
This medication stimulates the production of a group of fatty acids collectively called prostacyclin. This stimulation helps to block platelet activation.
Aspirin's effects and mechanisms of action vary with the dose given to the patient. This medication is sold under various brand names, such as Aspir, Ecotrin, Bayer and Easprin. Aspirin is often given to people experiencing a heart attack because it can quickly and powerfully inhibit platelet activity and the growth of the blood clot, thereby maintaining some measure of blood flow. Studies show that chewing the tablet has a faster effect than swallowing it.

Natural Blood Thinners

Natural blood thinners are any non-medication sources that slow or prevent blood clotting; however, these substances should not be used as a substitute for prescription anticoagulants or antiplatelets. These natural blood thinners might include alcohol and certain foods and herbs, such as garlic, ginger, celery seed and aniseed.

Even water can naturally thin the blood. Dehydration causes the blood to thicken, which can lead to an increased risk of clots. So drinking plenty of water can be good for cardiovascular health.

If you are taking blood thinner medications, you should check with your doctor before taking herbal supplements.

Combining blood thinner medications with natural blood thinners can result in an increased risk for bleeding and other unwanted side effects or complications.

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Foods to Limit When Taking Blood Thinners

Foods, herbs and spices, and oils containing high amounts of vitamin E, salicylates, natural antibiotics or omega-3 fatty acids have natural blood-thinning properties.

On the flip side, foods high in vitamin K can interfere with the way your blood thinner medication works, especially if you are taking warfarin.

Foods rich in vitamin K include leafy green vegetables, saturated fats, and cultured foods with live bacteria.

Foods to Limit while Taking Blood Thinners
  • Spinach
  • Kale
  • Swiss chard
  • Parsley
  • Cabbage
  • Endive
  • Vitamin E supplements
  • Asparagus
  • Dietary supplements with vitamin K

If you are already taking a blood thinner medication, you should talk to your doctor about any dietary concerns.

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Blood Thinners and Alcohol

Alcohol may interact with blood thinners by either decreasing or increasing the anticoagulation effects of the drugs. For example, people who drink while taking warfarin may be at risk of excessive bleeding because alcohol can enhance drug’s anticoagulation effects.

Alternately, chronic drinkers may metabolize warfarin more quickly, causing them to need a higher dose for the same therapeutic effect. Either way, warfarin and alcohol are a dangerous mix.

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Blood Thinner Side Effects

Possible side effects of blood thinners include uncontrolled internal bleeding, bruising and rash.

Get help immediately if:
  • Your urine turns dark red or dark brown
  • Your stools turn red, dark brown or black
  • You bleed more than normal during your period
  • You are coughing up blood
  • Your gums or nose bleeds and doesn’t stop quickly
  • You experience bad headaches or stomach pain that doesn’t go away
  • You are feeling sick, weak, faint or dizzy
  • You have an increase in bruises or blood blisters
  • You have a cut that doesn’t stop bleeding

Internal bleeding, or hemorrhaging, is an emergency condition that requires prompt medical attention.

Please seek the advice of a medical professional before making health care decisions.