South Bay Cardiovascular Center

Taking Your Medication


An anticoagulant is a medication that helps prevent blood from clotting (coagulating). These medications prevent new clots from forming or an existing clot from enlarging. They do not dissolve an existing blood clot. (These medications are often referred to as “blood thinners”, but they do not actually thin the blood.)

Because anticoagulants affect the blood's ability to clot, they can increase the risk of severe bleeding and heavy blood loss. It is very important to take these drugs exactly as directed and to see a physician regularly as long as they are prescribed.

Anticoagulants are often prescribed for people who have already suffered a heart attack or stroke to reduce their risk of developing another heart attack or stroke. They may also be prescribed for people who are at risk of developing blood clots, such as those with the following conditions.

  • Atrial fibrillation or artificial heart valves. These conditions increase the risk of clots forming in the heart and flowing to the brain where they can cause a stroke.
  • Deep vein thromboses (DVT). Clots, also called “thrombi”, can form in the leg veins. This may occur when someone is immobilized during a hospitalization or long airline flight.. These thrombi may break lose and become lodged in the blood vessels of the lung (pulmonary emboli). People at risk of developing deep vein thromboses may be prescribed anticoagulants
  • Blood clotting disorders (hypercoagulability)

How do Anticoagulants Work?

The body forms blood clots to control bleeding. These clots are created by platelets and proteins called "clotting factors". The clot-forming activity of platelets and clotting factors is usually kept in balance by clot-breaking proteins that remove the clots. An imbalance results in bleeding too easily (such as occurs in those with hemophilia), or the excessive formation of clots.

Anticoagulants decrease the activity of platelets or clotting factors and slow down the rate of clot formation.

Types of anticoagulants

There are several types of anticoagulants used to reduce the creation of blood clots. They are sometimes categorized by the part of the clotting system that they control. Anticoagulants, such as heparin and coumadin, reduce the activity of clotting factors in the blood. Antiplatelets, such as aspirin, clopidrogel (Plavix®) and ticlopdine (Ticlid®), prevent the platelets in the blood from clumping together.

There are also several new anticoagulants under development that are categorized as direct thrombin inhibitors.


Coumadin® (warfarin) is taken by mouth. It is usually taken once a day with or without food. Your doctor determines how much Coumadin you need by performing regular blood tests that monitors blood clotting. These tests include the Prothrombin Time (PT) and International Normalized Ratio (INR). Your dosage may change over time depending on the results of these tests.

The anti-clotting effects of Coumadin can be countered by the administration of vitamin K. This may be performed in emergency situations, such as when a person taking coumadin needs surgery.


Heparin® is administered by injection under the skin (subcutaneously) or intravenously (IV). It cannot be given by mouth. Heparin® provides immediate reduction in the clotting of the blood. It is often administered in a hospital setting with other anticoagulants before the other agents take effect.


Anticoagulant drugs must be taken exactly as directed by the physician. Taking too much of these medications can cause severe bleeding. Larger or more frequent doses should not be taken, and the drug should also not be taken for longer than prescribed.

Anticoagulants should also be taken on schedule. A record of each dose should be kept as it is taken. If a dose is missed, it should be taken as soon as possible followed by the regular dose schedule. However, a patient who forgets to take a missed dose until the next day should not take the missed dose at all and should not double the next dose, as this could lead to bleeding. A record of all missed doses should be kept for the prescribing physician who should be informed at the scheduled visits.

Persons who take anticoagulants should see a physician regularly while taking these drugs, particularly at the beginning of therapy. The physician will order periodic blood tests to check the blood's clotting ability. The results of these tests will help the physician determine the proper amount of medication to be taken each day.

Time is required for normal clotting ability to return after anticoagulant treatment. During this period, patients must observe the same precautions they observed while taking the drug. The length of time needed for the blood to return to normal depends on the type of anticoagulant drug that was taken. The prescribing physician will advise as to how long the precautions should be observed.

People who are taking anticoagulant drugs should tell all physicians, dentists, pharmacists, and other medical professionals who provide medical treatments or services to them that they are taking such a medication. They should also carry identification stating that they are using an anticoagulant drug.

Other prescription drugs or over-the-counter medicine, especially aspirin, should be not be taken without the prescribing physician being informed.

Because of the risk of heavy bleeding, anyone who takes an anticoagulant drug must take care to avoid injuries. Sports and other potentially hazardous activities should be avoided. Any falls, blows to the body or head, or other injuries should be reported to a physician, as internal bleeding may occur without any obvious symptoms. Special care should be taken in shaving and in brushing and flossing the teeth. Soft toothbrushes should be used and the flossing should be very gentle. Electric razors should be used instead of a blade.

Alcohol can change the way anticoagulant drugs affect the body. Anyone who takes this medicine should not have more than one to two drinks at any time and should not drink alcohol every day.

Anticoagulants may interact with many other medications. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be increased. Anyone who takes anticoagulants should inform the prescribing physician about other prescription or nonprescription (over-the-counter medicines) he or she is taking, even aspirin, laxatives, vitamins, and antacids.

Reference: The National Institute of Neurological Disorders and Stroke