Note: This page is undergoing revision. Everything on the page is accurate but we will be adding more information to this page. To learn more about this topic, please view the Stop the Clot Forum videos at This page will be updated shortly. See below for all approved oral anticoagulants (blood thinners).

Blood Clot Treatment

Anticoagulants: Treatment of Blood Clots

Anticoagulant medications (blood thinners).
Doctors use anticoagulants or blood thinners to treat blood clots.  These medications slow the time it takes for blood to clot. They also prevent clots from growing. Blood thinners also prevent more clots from forming in most patients. The most common blood thinners used today are heparin, low molecular weight heparin, and warfarin.

Unfractionated Heparin (UF)

UF Heparin is a fast-acting blood thinner. You may take heparin through a needle inserted in your vein (IV), or an injection under your skin. IV heparin works within minutes. You will probably get heparin by IV if you are in the hospital.

Monitoring heparin with daily blood testing.

If you take heparin, you will have a blood test every day to see if you are taking the right dose. This blood test is called a UF heparin level or anti-Xa level. The doctor will adjust your heparin dose based on the results of these blood test. Your blood levels can change. That is why you need frequent monitoring.

Advantages of heparin:

  • UF heparin does not cost a lot.
  • UF heparin gets into the blood quickly.
  • UF heparin works quickly to prevent your blood from forming blood clots.
  • The effect of UF heparin wears off quickly when the IV drip is stopped.

Disadvantages of UF heparin.

  • UF Heparin requires frequent blood tests to check how well the heparin is working to prevent your blood from clotting.
  • If you need to take UF heparin in your vein or by IV, you will need to be hospitalized.
  • To treat a new clot the doctor will put you in the hospital for 3-10 days.

Side effects of UF heparin.

The side effects of UF heparin include:

    • Bleeding (most serious side effect)
    • Skin rash
    • Headache
    • Cold symptoms
    • Stomach upset
    • Loss of bone strengthA rare side effect of UF heparin is a condition called Heparin Induced Thrombocytopenia (HIT).
      • Less common
      • May occur if you are on heparin for long periods of time, like several months
    • HIT is sometimes incorrectly called “heparin allergy.”
    • It occurs in a small number of patients.
    • It is very serious.
    • Symptoms include
    • Increased clotting or developing new clots while on heparin,
    • Which can lead to:
      • Deep vein thrombosis (DVT) or a clot in the leg or arm;
      • Pulmonary embolism or a blot clot in the lungs, or
      • Death.


Low molecular weight heparin are like heparin, but you can take them at home by giving yourself an injection or shot under the skin. They last longer in your body than UF heparin. The effect of LMWH is more predictable than UF heparin, so most patients do not need monitoring.

Names of LMWH.

The LMWH available in the United State are:

  • dalteparin (Fragmin®) and
  • enoxaparin (Lovenox®)

Advantages of LMWH.

  • LMWH is given by injection under the skin rather than by IV, so you can treat yourself at home more easily.
  • LMWH eliminates or reduces the time you need to spend in the hospital to treat a clot.
  • If you take LMWH, you usually do not have to have blood tests to monitor it.

Disadvantages of LMWH.

  • LMWH is expensive.
  • The side effects of LMWH are very similar to heparin; However, HIT and loss of bone strength are much less common than with heparin.


  • Warfarin (Coumadin®) is a pill for long-term anticoagulation or blood thinning.
  • You usually take heparin (UF heparin or LMWH) for the short-term.
  • The doctor adds warfarin with the heparin (UF heparin or LMWH heparin) so you take both medicines for a few days.
  • The warfarin must reach a certain level in your blood to work.
  • You may have to take warfarin 5-7 days (or longer) with the heparin (UF heparin or LMWH heparin) for the warfarin to reach an adequate level in your blood to work.
  • Once your warfarin dose is sufficient, the doctor will stop your heparin (UF heparin or LMWH heparin) and you can go home from the hospital.

Advantages of warfarin.

  • Warfarin is inexpensive.
  • Warfarin is a pill.
  • Warfarin is familiar to doctors because it has been used to treat patients since the 1950’s.

Disadvantages of warfarin.

  • If you take Warfarin, the most serious side effect is bleeding because Warfarin lengthens the time it takes for blood to clot.
  • You may experience the following side effects:
    • Headache (rare)
    • Rash
    • Hair loss
    • Skin breakdown
    • Purple toes
    • Elevated liver enzymes
  • You should discuss any side effects or unusual symptoms with your healthcare provider as soon as you notice them.
  • Sometimes these side effects go away by themselves.
  • If the side effects do not go away, your doctor may prescribe a different blood thinner.

Monitoring warfarin with regular blood tests.

  • The blood test that monitors warfarin is called an INR (international normalized ratio).
    • The INR measures how long it takes blood to clot.
    • It standardizes results of prothrombin time, protime, or clotting time (names for different types of tests used in different labs).
    • Most patients on warfarin do best with an INR between 2.0 and 3.0, considered the ideal or “therapeutic range.”
    • A higher or lower INR range may be appropriate for certain patients.
  • Warfarin requires frequent monitoring  (INR), especially in when you start taking it.
  • Once your INR is stable you can have your blood tests about once a month to monitor.
  • INR can be measured by going to the lab and having a blood test, or by a finger stick test that can be performed in a clinic or at home with an INR  a self-monitoring device.
    • Home INR testing requires patients meet certain requirements
    • Home INR testing can be expensive
  • INR too low? If an INR is below the ideal or therapeutic range, the risk of clotting is higher.
  • INR too high? If an INR is above the therapeutic range, the risk of bleeding is higher.

Tips for taking warfarin.

  • Same time each day.
    • You should take warfarin the same time every day.
    • The evening is the best time to take warfarin because you can change the dose the day of the INR if needed.
    • If the evening is not a convenient time, take it at the same time each day that fits your schedule, or with the same task each day that will help you remember.
  • Missed Doses.
    • If you miss a dose of warfarin, you have an 8-hour window when it is still safe to take it.
    • If you skip your dose and more than 8 hours goes by, contact your doctor right away.
  • Warfarin and alcohol.
    • Drinking a light or moderate amount of alcohol (1-2 glasses of wine or 1-2 beers per day) usually does not influence the INR.
    • However, drinking a large amount can affect warfarin and increase your risk for bleeding.
  •  Warfarin and food.
    • Food high in vitamin K, like green leafy vegetables can affect the amount of warfarin you need to take.
    • You must keep a consistent diet of foods high in vitamin K such as green leafy vegetables, since if you change the amount of vitamin K you eat, it affects your INR levels.

Effect of other prescribed or over-the-counter medications on warfarin.

  • ANYTIME you start or stop a medicine – even if it is something you bought over the counter – you should tell your doctor, nurse or pharmacist right away because they may want to start checking your warfarin level more frequently.
  • Tell your doctor, nurse, or pharmacist about all the medications you take. This includes prescription drugs, over the counter ones, and vitamins, herbals and supplements.
  • Some medications, especially antibiotics, can change your INR reading.
  • Over-the-counter anti-inflammatory medications (such as aspirin, ibuprofen, naprosen, goody’s powder) may increase your risk of bleeding.
  • You can usually take acetaminophen (Tylenol®). Tell your doctor if you take acetaminophen more than once a day or for longer than a week.

Tell Your Doctor All the Medications You Take

  • Herbal medicines can interact with warfarin and may change your INR.
  • Some have anticoagulant effects and may put you at greater risk for bleeding.
  • Herbal products do not always list all of their ingredients and may not work as advertised.
  • If you take herbal medication, tell your doctor which ones you take.

New Anticoagulant or Anti-Clotting Medications

Several new anticoagulants (blood thinners) medications have recently been approved by the United States Food & Drug Administration (FDA). 

Approved (in US) to treat prevent blood clots that can cause strokes in people who have atrial fibrillation or AFib:

  • Apixaban (Eliquis®)
  • Dabigatran (Pradaxa®), and
  • Rivaroxaban (Xarelto®)

Approved (in US) to treat deep veins thrombosis (leg or arm clot or DVT) & pulmonary embolism (lung clot or PE)

  • Rivaroxaban  (Xarelto®)
  • Apixaban (Eliquis®)  – Approved for prevention of DVTs/PEs following hip and knee replacement surgery as of March 14, 2014.
  • Dabigatran (Pradaxa®) – Approved for for the treatment of deep venous thrombosis (DVT) and pulmonary embolism (PE) in patients who have been treated with a parenteral anticoagulant for 5 to 10 days, and to reduce the risk of recurrent DVT and PE in patients who have been previously treated as of April 7, 2014.
  • Other medications are being reviewed for approval from the FDA and may be available within the next year

Facts about these newer medications: They

  • Do not require frequent lab monitoring
  • Have less drug/herbal interactions
  • Require dietary restrictions
  • Have less fatal bleeding events
  • Are expensive
  • Do not have antidotes meaning their anti-clotting properties are not easily reversible – may require transfusion with clotting factor
  • Take effect quickly and do not require overlapping with heparin
  • Effects wear off quickly
  • May be eliminated through the kidneys or liver

Your medication decision will depend on your individual circumstances. Ask your doctor, nurse, or pharmacist questions whether the new medications are right for you.

Updated April, 2014



The Medical and Scientific Advisory Board

Authors of previous versions:

Lisa Anselmo PharmD, BCOP

Edward Libby MD

Stephan Moll MD

Sara Critchley RN MS