Heparin is an anticoagulant you take to prevent blood clots or keep an existing clot from getting worse. People often receive heparin through an IV during a hospital stay, but you can also inject it into your skin. People take heparin for different lengths of time, depending on why they need it. Heparin works quickly but also wears off quickly.


What is heparin?

Heparin is an anticoagulant (“blood thinner”) that stops your blood from forming blood clots or making them bigger. It can help a blood clot dissolve faster, but it can’t break it down.

Your digestive system can’t absorb heparin, so you need to receive it a different way. A heparin infusion goes into your body through an IV in your vein. You can also inject it below your skin.

How does heparin work?

Heparin makes your blood less able to clot. To do this, it makes thrombin inactive. Thrombin has a major role in the clot-making process. Heparin also blocks factor Xa, another clotting factor in your blood, preventing it from playing its part in making clots. Imagine if your body used an assembly line to make clots; heparin would be taking tools away from two workers with important jobs on the line.

What is heparin used for?

Healthcare providers use heparin to treat or prevent blood clots that can cause you harm. You may receive heparin if you have:

You may be on heparin temporarily while you’re in the hospital if you have a mechanical heart valve or an acquired or genetic condition that makes you prone to forming blood clots.

Sometimes, pregnant people may need heparin if there’s a concern about losing the fetus. (Heparin doesn’t go through the placenta to a fetus.)


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Procedure Details

What happens when you receive heparin?

When a healthcare provider gives you heparin as an infusion through an IV line, they have to draw and test your blood first. Your test results tell them the correct amount of heparin to give you.

An activated partial thromboplastin time (aPTT) test tells how long it takes for your blood to clot. If you already have heparin in your body, your provider will check to see how well it’s working. They’ll adjust your heparin dose and test regularly to ensure the heparin is working correctly.

When they need fast results, providers use an activated clotting time (ACT) test.

You may receive infusion therapy in a hospital or even at home. Your provider will give you the information you need if you’re having infusion therapy at home.

How long will I need heparin?

The amount of time that you need heparin depends on why you’re taking it. For example, after surgery, you may need heparin for seven days or until you can prevent blood clots by walking around.

Healthcare providers use heparin in a hospital setting. Before you leave the hospital, they’ll switch you over to a different medicine that doesn’t need an IV or injection. When you go home from the hospital, you’ll probably be taking a type of blood thinner that you can swallow instead of giving yourself injections.

Risks / Benefits

What are the potential benefits of heparin?

Heparin’s benefits include:

  • Working quickly.
  • Wearing off quickly.
  • Being reversible with a heparin antidote called protamine.
  • Having a multidecade history of use.


What are the risks or complications of heparin?

If you get hurt when you have heparin in your body, you may bleed too much. When you’re taking heparin, report any concerns about bruising or bleeding to your provider right away. If you’re in the hospital or another healthcare facility, ask for help before getting out of bed. This’ll reduce the risk of falling.

If you receive a very high dose of heparin, there’s also the risk of spontaneous bleeding in your brain, nose, lungs, gastrointestinal (GI) tract, urinary tract or large muscles in your body such as your psoas muscle, quadriceps or abdominal muscles.

Also, other drugs can change the way heparin works. Your dose of the medicine may get too weak or too strong if it reacts to another drug you’re taking. Check with your healthcare provider or pharmacist before you start to take any new drugs, over-the-counter products or supplements.

Side effects of heparin may include:

Recovery and Outlook

How quickly does heparin work?

When you receive heparin through an IV, it works right away. A heparin injection under your skin starts working in one or two hours.


Is there anything I can do to make this treatment easier on me?

If you do need to give yourself a heparin injection, your healthcare provider will show you how to do it. They can tell you where to inject it and what to do with the needles you use.

When To Call the Doctor

When should I call my healthcare provider?

Contact your provider if you’re taking heparin and you have these side effects:

  • Trouble breathing, fast breathing or wheezing.
  • Bleeding that won’t stop.
  • Bruising, rash or patches on your skin.
  • Sudden weakness or numbness on one side of your body.
  • Balance issues or confusion.
  • Problems seeing or hearing.
  • Headaches.
  • Pain in your chest or a fast heart rate.
  • Coffee ground-like vomit.
  • Stools (poop) that are black, tarry or bloody.
  • Urine (pee) that looks brown or red.

A note from Cleveland Clinic

If your healthcare provider orders heparin for you during a hospital stay, you can take comfort in knowing that hospitals have been using it for decades. They have tests to help them determine how much you need so they give you the right amount. Like any medicine, heparin has side effects and risks. But your provider won’t prescribe it without looking at the benefits and risks in your situation. Talk to your provider if you have questions about taking heparin.

Medically Reviewed

Last reviewed on 06/02/2023.

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