By Angela Ryan Lee, MD 

 Medically reviewed by Anisha Shah, MD

Blood thinners are medications used to treat and prevent blood clots. Blood travels through blood vessels in a liquid form to bring oxygen and nutrients to tissues throughout the body. When blood clots form in the body, they block normal blood flow from reaching tissues, and can cause tissue death, such as in heart attack, stroke, and pulmonary embolism.

While blood thinners can be lifesaving medications, they carry a risk of bleeding. This article discusses the types of blood thinners, their medical uses, and side effects.

Daniel Grill / Getty Images

What Are Blood Thinners?

Blood thinners are medications that treat and prevent blood clots. Blood clots are semi-solid clumps of red blood cells, platelets, fibrin (a type of protein), and other proteins.

Blood clotting is an extremely important function of the body that prevents bleeding. Without blood clotting, a small cut would cause serious, prolonged bleeding.

Thrombus vs. Embolus

Another word for blood clot is "thrombus," but when a blood clot travels to another place in the body, it is known as "embolus." For example, a "pulmonary embolism" is a blood clot that has traveled from the deep veins in the leg to the arteries in the lung.

Blood clots form through two important processes: the coagulation cascade and platelet activation. Blood thinners work by targeting steps in each of these processes.

In the coagulation cascade, damaged tissue sets off a cascade of events that activates several proteins in the blood, called clotting factors. These proteins are activated through a series of steps that, ultimately, activates fibrin. Fibrin is a protein formed during the clotting process that helps stop blood flow.

Another important part of blood clots is platelets. Damaged tissue activates platelets in the blood. Activated platelets attract other platelets, and they stick to each other to plug up the wound and stop the bleeding.

Red vs. White Clots

Blood clots rich in red blood cells and fibrins are known as "red clots," whereas those rich in platelets, which are colorless, are referred to as "white clots." Red clots are found in veins (like the leg veins), whereas white clots are found more in arteries (like the coronary arteries of the heart). The distinction of red vs. white is based on the color and composition of the clots, but all clots contain varying amounts of platelets, fibrin, and red blood cells.

Why Are Blood Thinners Prescribed?

In a broad sense, blood thinners are used to treat blood clots or prevent blood clots from forming when they are dangerous to the body. The following are some specific conditions that could require blood thinners:12

• Deep vein thrombosis (DVT), a blood clot in the leg veins

• Pulmonary embolism (PE), a blood clot in the pulmonary blood vessels

• Acute coronary syndrome, a blood clot in the coronary arteries that causes heart attacks

• Prosthetic heart valves

• Left ventricular thrombus, a blood clot in the heart

• Acute limb ischemia, a blood clot in a leg artery

• Acute mesenteric ischemia, a blood clot in the artery feeding the bowel

• Atrial fibrillation, an irregular and unusually rapid heartbeat

• Hypercoagulable state, conditions that cause thick blood

• Certain pregnancy-related conditions3

• Prevention of blood clots after certain surgeries

How Do Blood Thinners Work?

In general, all blood thinners work by either blocking or inactivating part of the system that forms blood clots. These medications work by binding to proteins that are involved in either the coagulation cascade or to proteins on platelet surfaces.

Anticoagulant medications target the coagulation cascade, whereas antiplatelet medications target platelet activation.

Types of Blood Thinners

Anticoagulants

Anticoagulant blood thinners target various proteins in the coagulation cascade. These medications are used for treating red clots, like deep vein thrombosis and pulmonary embolism, as well as preventing strokes in atrial fibrillation and mechanical heart valves.

Anticoagulants are also used during acute blood clotting in arteries (such as heart attacks, acute limb ischemia, and acute mesenteric ischemia). Examples of anticoagulants include:

• Coumadin (warfarin)

• Enoxaparin (low molecular weight heparin)

• Factor X inhibitors, such as Eliquis (apixaban) and Xarelto (rivaroxaban)

• Direct thrombin inhibitors, such as Acova (argatroban), Angiomax (bivalirudin), and Pradaxa (dabigatran)

• Tissue plasminogen activators such as Actilyse (alteplase), TNKase (tenecteplase), and Retavase (reteplase)

Antiplatelets

Antiplatelets are medications that target the activation and aggregation of platelets. They are commonly used in the treatment and prevention of stroke and heart attacks.

Antiplatelets are also used to protect stents placed in the heart's coronary arteries and other arteries (such as carotid arteries of the neck and leg arteries in peripheral arterial disease).

Examples of antiplatelets include:

• Aspirin

• P2Y12 receptor blockers, such as Plavix (clopidogrel), Effient (prasugrel), and Brillinta (ticagrelor)

• Phosphodiesterase inhibitors like Aggrenox (dipyridamole and aspirin) and Pletal (cilostazole)

• GIIb/IIIa inhibitors, such as Reopro (abciximab), Integrilin (eptifibatide), and Aggrastat (tirofiban)

Side Effects

Unsurprisingly, the main side effect of blood thinners is bleeding. People who take blood thinners will notice that a cut or nick takes longer to stop bleeding and that they bruise more easily. But serious bleeding, such as bleeding in the gastrointestinal tract or brain, can occur. These bleeds can be life-threatening.

Each specific drug has a list of side effects that can range from nausea, constipation, and headache, to shortness of breath and severe allergic reaction.

Natural Blood Thinners

Some foods and supplements are believed to have some blood thinning properties. However, they are not regulated by the Food and Drug Administration (FDA), and the concentration of active compounds in supplements is not consistent.

Always discuss any supplements you're taking or considering with your healthcare provider, as they can interfere with other medications. Supplements should never be taken as a replacement for a prescribed blood-thinning medication.

The following have some evidence of blood-thinning properties:4

• Cranberry

• Dong quai

• Fenugreek

• Feverfew

• Garlic

• Ginger

• Ginkgo

• Red Clover

• Turmeric

• White willow

Summary

Blood thinners are important medications used for treating and preventing blood clots. These include anticoagulant and antiplatelet medications. The benefit of taking blood-thinning medications must always be weighed against their risk of serious bleeding.

Sources

MedlinePlus. Blood thinners.

Sugerman DT. Blood thinners. JAMA. 2013;310(23):2579. doi:10.1001/jama.2013.282755

American College of Obstetricians and Gynecologists. Low-dose aspirin use during pregnancy. ACOG Committee Opinion No. 743. Obstet Gynecol. 2018;132:e44–52.

Leite PM, Martins MAP, Carvalho MDG, Castilho RO. Mechanisms and interactions in concomitant use of herbs and warfarin therapy: An updated review. Biomed Pharmacother. 2021;143:112103. doi:10.1016/j.biopha.2021.112103

Reed GW, Abdallah MS, Shao M, Wolski K, et al. Effect of Aspirin Coadministration on the Safety of Celecoxib, Naproxen, or Ibuprofen. J Am Coll Cardiol. 2018 Apr;71(16):1741-1751. doi: 10.1016/j.jacc.2018.02.036

By Angela Ryan Lee, MD
Angela Ryan Lee, MD, is board-certified in cardiovascular diseases and internal medicine. She is a fellow of the American College of Cardiology and holds board certifications from the American Society of Nuclear Cardiology and the National Board of Echocardiography. She completed undergraduate studies at the University of Virginia with a B.S. in Biology, medical school at Jefferson Medical College, and internal medicine residency and cardiovascular diseases fellowship at the George Washington University Hospital. Her professional interests include preventive cardiology, medical journalism, and health policy.