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Blood Thinners

Also called: Anti-platelet drugs, Anticoagulants
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What are blood thinners?

Blood thinners are medicines that prevent blood clots from forming. They do not break up clots that you already have. But they can stop those clots from getting bigger. It's important to treat blood clots, because clots in your blood vessels and heart can cause heart attacks, strokes, and blockages.

Who needs blood thinners?

You may need a blood thinner if you have:

What are the different types of blood thinners?

There are different types of blood thinners:

  • Anticoagulants, such as heparin or warfarin (also called Coumadin), slow down your body's process of making clots.
  • Antiplatelets, such as aspirin and clopidogrel, prevent blood cells called platelets from clumping together to form a clot. Antiplatelets are mainly taken by people who have had a heart attack or stroke.

How can I take blood thinners safely?

When you take a blood thinner, follow the directions carefully. Blood thinners may interact with certain foods, medicines, vitamins, and alcohol. Make sure that your health care provider knows all of the medicines and supplements you are using.

You may need regular blood tests to check how well your blood is clotting. It is important to make sure that you're taking enough medicine to prevent clots, but not so much that it causes bleeding.

What are the side effects of blood thinners?

Bleeding is the most common side effect of blood thinners. They can also cause an upset stomach, nausea, and diarrhea.

Other possible side effects can depend on which type of blood thinner that you are taking.

Call your provider if you have any sign of serious bleeding, such as:

  • Menstrual bleeding that is much heavier than normal
  • Red or brown urine
  • Bowel movements that are red or black
  • Bleeding from the gums or nose that does not stop quickly
  • Vomit that is brown or bright red
  • Coughing up something red
  • Severe pain, such as a headache or stomachache
  • Unusual bruising
  • A cut that does not stop bleeding
  • A serious fall or bump on the head
  • Dizziness or weakness

Start Here

  • Anti-Clotting Agents Explained (American Stroke Association)
  • Anticoagulants (Texas Heart Institute) Also in Spanish
  • Anticoagulants and Drug-Food Interactions (National Jewish Health)
  • Blood Thinner Pills: Your Guide to Using Them Safely (Agency for Healthcare Research and Quality) Also in Spanish
  • What Are Anticoagulants and Antiplatelet Agents? Easy-to-Read (American Heart Association) - PDF
  • What You Need to Know When Taking Anticoagulantion Medication (National Jewish Health) - PDF

Diagnosis and Tests

Related Issues

  • Blood Thinners and Dental Care (American Academy of Oral Medicine)
  • Blood Thinners: Can I Still Get Blood Clots? (Mayo Foundation for Medical Education and Research) Also in Spanish
  • Bridging Anticoagulation: Is it Needed When Warfarin Is Interrupted Around the Time of a Surgery or Procedure? (American Heart Association)
  • Heparin-Induced Thrombocytopenia (American Heart Association) - PDF
  • Medication Interactions: Food, Supplements, and Other Drugs (American Heart Association)
  • Prothrombin Time Test and INR (PT/INR) From the National Institutes of Health (National Library of Medicine) Also in Spanish
  • Warfarin Side Effects: Watch for Interactions (Mayo Foundation for Medical Education and Research) Also in Spanish


  • Anticoagulation (Blood Thinners) and Congenital Heart Defects (American Heart Association)
  • Antiplatelet Therapy (Texas Heart Institute) Also in Spanish
  • Daily Aspirin Therapy: Understand the Benefits and Risks (Mayo Foundation for Medical Education and Research) Also in Spanish
  • Patient's Guide to Taking Warfarin (American Heart Association)


Clinical Trials

  • ClinicalTrials.gov: Anticoagulants From the National Institutes of Health (National Institutes of Health)
  • ClinicalTrials.gov: Heparin From the National Institutes of Health (National Institutes of Health)
  • ClinicalTrials.gov: Platelet Aggregation Inhibitors From the National Institutes of Health (National Institutes of Health)
  • ClinicalTrials.gov: Warfarin From the National Institutes of Health (National Institutes of Health)

Journal Articles References and abstracts from MEDLINE/PubMed (National Library of Medicine)

  • Article: Heparin and heparin proteoglycan-mimetics activate platelets via PEAR1 and PI3Kβ.
  • Article: Warfarin Time in Therapeutic INR Range and Direct Oral Anticoagulant Adherence...
  • Article: Direct Oral Anticoagulants versus Vitamin K Antagonists in Individuals Aged 80...
  • Blood Thinners -- see more articles

Find an Expert

  • National Heart, Lung, and Blood Institute From the National Institutes of Health

Patient Handouts

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.