Although anticoagulants are called blood thinners, these medicines do not really thin your blood. Instead, they decrease the blood's ability to clot. Decreased clotting keeps fewer harmful blood clots from forming and from blocking blood vessels.

Why do I need to take an anticoagulant?

  • These medicines reduce your risk for heart attackstroke, and blockages in your arteries and veins by preventing clumps of blood (blood clots) from forming or growing. However, anticoagulants cannot break up blood clots that have already formed.
  • Your doctor may prescribe an anticoagulant if you have had a heart valve replaced or if you have atrial fibrillationphlebitiscongestive heart failure, or, in some cases, if you are obese.

How do anticoagulants work?

  • Although anticoagulants are called blood thinners, these medicines do not really thin your blood. Instead, they decrease the blood’s ability to clot. Decreased clotting keeps fewer harmful blood clots from forming and from blocking blood vessels.
  • Oral anticoagulants come in a pill form that you swallow. Note: Other more powerful anticoagulants, such as heparin, need to be injected by a needle into your bloodstream. These kinds of anticoagulants will be given to you in the hospital, where you can be closely watched for complications. A form of heparin (called low molecular weight heparin) may be prescribed for you to take at home, under your doctor’s supervision.

How much do I take?

There are different kinds of anticoagulants. The amount of medicine that you need to take may vary. Talk to your doctor or pharmacist for more information about how and when to take this medicine.

What if I am taking other medicines?

Other medicines that you may be taking can increase or decrease the effect of anticoagulants. These effects are called an interaction. Be sure to tell your doctor about every medicine and vitamin or herbal supplement that you are taking, so he or she can tell you about any interactions.

The following are categories of medicines that can increase or decrease the effects of anticoagulants. Because there are so many kinds of medicines within each category, not every type of medicine is listed by name. Tell your doctor about every medicine that you are taking, even if it is not listed below.

  • Aspirin
  • Acetaminophen (e.g., Tylenol, Excedrin)
  • Ibuprofen (e.g., Motrin, Advil, Nuprin)
  • Ketoprofen (e.g., Orudis, Orudis KT)
  • Naproxen (e.g., Aleve)
  • Medicines to treat an irregular heartbeat (antiarrhythmics)
  • Antacids
  • Corticosteroids or other cortisone-like medicines
  • Antidepressants
  • Antihistamines
  • Calcium and vitamin K supplements
  • Sleeping pills
  • Certain antibiotics
  • Certain medicines used to treat convulsions
  • Medicines used to treat an overactive thyroid
  • Certain antifungal medicines

While taking anticoagulants, you should also avoid smoking and drinking alcohol. Also, watch your diet. Large doses of vitamin K (found in fish, liver, and spinach, cabbage, cauliflower, brussels sprouts, and other green, leafy vegetables) can decrease the effects of the medicine. This does not mean that you should stop eating these foods, just be careful not to eat too much of them.

You should have your blood tested regularly so doctors can monitor how your blood is clotting.

What else should I tell my doctor?

Talk to your doctor about your medical history before you start taking an anticoagulant. The risks of taking the medicine need to be weighed against its benefits. Here are some things to consider if you and your doctor are deciding whether you should take this medicine.

  • You have allergies to foods or dyes.
  • You are thinking of becoming pregnant, you are pregnant, or you are breast-feeding your baby.
  • You are over 60. Younger people tend to have fewer problems while taking an anticoagulant.
  • You have an aneurysm.
  • You have recently had surgery, or you are going to have surgery in the next 2 months (including dental surgery).
  • You have had a stroke or a transient ischemic attack (TIA or “mini stroke”) or you have a history of bleeding in the brain.
  • You have a stomach ulcer or other stomach problems.
  • You have high blood pressure.
  • You have kidney or liver disease.
  • You have thyroid disease.
  • You have cancer.
  • You have diabetes.
  • You have high cholesterol.
  • You have hemophilia or other bleeding problems.
  • You have recently fallen or hit your head.
  • You have cuts or open wounds.
  • Your menstrual periods are heavy or they last a long time.
  • You participate in sports or other activities that put you at risk for bleeding or bruising.

What are the side effects?

Sometimes a medicine causes unwanted effects. These are called side effects. Not all of the side effects for anticoagulants are listed here. If you feel these or any other effects, you should check with your doctor.

Common side effects:

  • Bloating and gas
  • Diarrhea
  • Upset stomach or throwing up
  • Feeling less hungry

Less common side effects:

  • Coughing up or throwing up blood
  • Dark stools
  • A skin rash, hives, or itching
  • Sore throat
  • Hair loss
  • Bruising more often
  • Back pain
  • Fever, chills, or weakness
  • Yellowing of the skin or eyes (jaundice)

Rare side effects:

  • Headache
  • Dizziness
  • Shortness of breath
  • Mouth sores or bleeding gums
  • Purple coloring to your fingers or toes

Again, tell your doctor right away if you have any of these side effects. Do not stop taking your medicine unless your doctor tells you to. If you stop taking your medicine without checking with your doctor, it can make your condition worse.
A consumer-based site by the American Society of Health-System Pharmacists that provides information about all types of medicines as well as safety tips for their proper use. The site’s search feature lets users search medicines by the brand or generic name.

The information in this Medicines for Cardiovascular Disease section has been taken from a number of sources. It is meant to give you information about certain medicines, but it does not cover all of the possible uses, warnings, side effects, or interactions with other medicines and vitamin or herbal supplements. This information should not be used as medical advice for individual problems. Please talk to your doctor and/or your pharmacist for prescription instructions.