Unfractionated Heparin for Deep Vein Thrombosis

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Unfractionated Heparin for Deep Vein Thrombosis


Generic Name
unfractionated heparin

How It Works

Normally, when an injury that causes bleeding occurs, the body sends out signals that cause blood to clot at the wound, and then the clot naturally breaks down as the wound heals. A person prone to abnormal clotting has an imbalance between clot formation and clot breakdown.

Anticoagulant medicines prevent new clots from forming and prevent existing clots from growing (extending) by stopping the production of certain proteins that are needed for blood to clot. They do not break up or dissolve existing blood clots.

Why It Is Used

Unfractionated heparin is typically only used in the hospital. It is used to prevent and initially treat a deep vein thrombosis.1

Unfractionated heparin (UH) is given through a vein (intravenously, or IV) or injected under the skin.

When used for prevention, heparin might be injected a few hours before surgery. It might be given for a few days after surgery.

When used for treatment, heparin might be given through an IV or an injection.

After getting unfractionated heparin in the hospital, you will likely start taking other types of anticoagulants at home, such as low-molecular-weight heparin and warfarin.

How Well It Works

Heparin can be used to treat or prevent a deep vein thrombosis. When used for treatment, heparin prevents new blood clots from forming and prevents existing clots from getting larger. This allows the normal body systems to dissolve the clots that are already formed.

Heparin reduces the chance that a blood clot will get larger. This reduces the risk of getting a blood clot in the lung (pulmonary embolism).

Side Effects

Unfractionated heparin can cause serious bleeding inside your body. But you will be watched closely, because it is typically given only in the hospital. Your medical team will watch you closely for signs of bleeding or other problems. You will get regular blood tests to check the effects of the medicine.

For your safety, heparin can be turned off quickly if it is given through an IV. This method is safe for people who might bleed or need procedures done in an emergency.

Side effects often happen at injection sites. These side effects include:

  • Pain.
  • Irritation.
  • Bruising.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

If you are pregnant and you need to take an anticoagulant, you will take a type of heparin during your pregnancy. Heparin has not been shown to affect the fetus.

For more information, see Pregnancy and the Increased Risk of Developing Blood Clots.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Antithrombotic drugs (2011). Treatment Guidelines From The Medical Letter, 9(110): 61–66.


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerJeffrey S. Ginsberg, MD - Hematology
Last RevisedDecember 28, 2011

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