Blood Thinners: Differences Between Anticoagulants, Thrombolytics, and Antiplatelets


There are a number of drugs that people refer to as "blood thinners".  Blood thinners are actually are variety of types of drug.  Each type of blood thinner works in a different way and will help different conditions.  Most blood thinner do not actually thin the blood.  A few ways that blood thinners can work by keeping blood from sticking together, breaking up clotted blood, or changing the way that blood behaves.  This site will explain some of the different drug classes that often fall under the heading of "blood thinner".  It will also give tips for using some of the different medications.  It does not replace a doctor's advice.  I am not a doctor.  I don't even play one on television. 

How does blood clot?

Blood clotting is a complex process that involves four things: platelets, clotting factors, fibrin (a webby, mesh-like substance), and other cells. Platelets and clotting factors float around in your blood all the time.

Blood also contains substances that prevent blood clots. These substances are called anticoagulants. It is the balance of these substances in the blood that allow blood to clot as needed and only when needed.

Clotting factors and anticoagulants are made in the liver. They have the ability to turn on or turn off as needed. When they turn on, the fibrin can activate and turn into a net that covers the place that is torn and bleeding. The fibrin web catches platelets and other blood cells to form a strong patch that can allow the body to stop bleeding and begin to heal. When blood clots are not needed, the body makes anticoagulant to prevent the clots and also creates enzymes to dissolve any unneeded clots.

Each drug class that works on blood clots works on a different part of the clotting sytem.  The name blood thinner is not very descript as blood thinning is very different from preventing or treating clots. 

Differences between venous and arterial clots

Treating arterial versus venous clots

Anticoagulants: vitamin K antagonists (warfarin), heparin, low molecular weight heparins, heparinoids

Anticoagulants work by interfering with the formation of the fibrin web. They affect the various clotting factors that the liver produces. Venous clots are caused when stationary blood develops unneeded fibrin webs. For this reason, anticoagulants are the best choice for venous clots. Examples of venous clots include a deep vein thrombosis or a pulmonary embolism. This class of drugs is used when these types of clots are showing up. It is also used when an individual has a condition that affects the fibrin and clotting factors. An example is Factor V Leiden.

Warfarin chemical structure - thanks to Vitualis on Flickr
Warfarin chemical structure - thanks to Vitualis on Flickr

Vitamin K antagonists: anisindione, Miradon, warfarin, Coumadin, Jantoven, Marevan, Waran, and others

Vitamin K antagonists works by interfering with vitamin K. Vitamin K is used by the liver to create clotting factors and anticoagulants. There are a number of different drugs in this class. Vitamin K antagonists have been around for over 50 years and have had a lot of development. In the United States, warfarin is the mainstay of anticoagulation. It is very rare to see another vitamin K antagonist used in treatment. If a patient is allergic to warfarin, the other antagonists can be considered. This section will focus only on wafarin; however, much of the information here applies to the other vitamin K antagonists as well.

Warfarin impairs the hepatic synthesis of factors II, VII, IX, and X. Because warfarin interferes with both clotting and anticoagulation, patients must use another medication for the first 5 days on warfarin therapy. Heparins and low molecular weight heparins are the drugs currently used to initiate warfarin. These drugs will prevent a blood clot from forming when starting warfarin. If warfarin is not started with an additional anticoagulant, it is likley that the patient will experience blood clots. As warfarin works by interfering with vitamin K, a consistent amount of this vitamin must be consumed every day. Warfarin is monitored by testing that is referred to as an INR test or protime. This test will see how long it takes the blood to clot. Each patient has a target INR. Dose will be adjusted to maintain this target. Common side effects are bleeding, anemia, hair loss, and osteoporosis. Warfarin can not be taken during pregnancy.

  • Warfarin is very inexpensive
  • Warfarin requires additional medication the first 5 days
  • Warfarin must be monitored by regular INR tests
  • Warfarin users must consume a consistent amount of vitamin K
  • Changes in diet or medication require extra INR testing
  • Warfarin can not be used in pregnancy

A Lovenox syringe from A Boy and His Bike on Flickr.
A Lovenox syringe from A Boy and His Bike on Flickr.

Low molecular weight heparins: Normiflo (ardeparin), Fragmin (dalteparin), Orgarin (danaparoid), Lovenox (enoxaparin), Innohep (tinzaparin)

Low molecular weight heparins (LMWH) also fall under the anticoagulant category. They inhibit Factors Xa and IIa. Some examples in this class are Normiflo (ardeparin), Fragmin (dalteparin), Orgarin (danaparoid), Lovenox (enoxaparin), and Innohep (tinzaparin). All of these drugs are administered by injection. They can be done at home and can come in vials or pre-filled syringes. Some people may feel squeamish about self-injecting. I know I was worried at first. The needle on my pre-filled Lovenox syringes were very sharp and went in smoothly without effort. LMWH can be used when a patient is starting a warfarin regimen. This will prevent clots during the beginning of warfarin anticoagulation. LMWH also can be used as a stand alone treatment or prevention of blood clots. This drug class has some additional unique uses. It can be used as a prophylactic before a long haul flight or car trip to prevent clots, it can be used during pregnancy to help someone with a clotting condition to carry the baby to term without complications, and it can be used as a bridge therapy so that warfarin is cleared out of the body prior to surgery. One of the best parts of these medications is that the patient does not need blood tests to assess blood levels. The down side is that this class is very new and is high cost.

  • Low molecular weight heparins do not need blood monitoring
  • Low molecular weight heparins can be used to initiate warfarin
  • Low molecular weight heparins are useful in pregnancy
  • Low molecular weight heparins can be used at home
  • Low molecular weight heparins can be expensive

Tips on giving yourself LMWH

Ice, ice, ice. Low molecular weight heparins cause deep bruises where the shot is given. There are some ways to minimize this side effect. Ice the area for the injection until it is nice and numb. The ice will lessen the pain from the injection and it will also prevent the bruising. After the injection is done, put pressure on the site for at least 10-15 seconds. This will help to stop any subcutaneous bleeding. If the location is sore, ice it for an additional period after the injection. You may consider icing it longer if you have a very sore, large bruise. For more detailed directions, see the link below.

Direct Thrombin Inhibitors: Pradaxa (dabigatran), hirudin, bivalirudin, lepirudin, desirudin, argatroban

The direct thrombin inhibitor class has some of the newest anticoagulants on the market. They work by binding to the thrombin molecule. Thrombin is a protein that is involved in clotting. It activates many of the clotting factors, including Factor V. There are two ways in which direct thrombin inhibitors act. They can bind to thrombin on the active site (univalent) or on both the active site and exosite 1 (bivalent). Bivalent DTIs may be used in circumstances in which heparin is indicated but not available as an option. They are administered by injection and are not used for long term anitcoagulation. Argatroban is a treatment option when a patient experiences a very rare, life threatening complication of heparin known as heparin-induced thrombocytopenia. Dabigatran (Pradaxa) is the most common of this class. Pradaxa is a recently approved medication and is affective for stroke prophylaxis and atrial fibrillation. The benefit of Pradaxa is that it does not require routine blood monitoring. (Currently, there is no standardized test available to measure the anticoagulant effects of this class of drugs.) The largest problem with this class of drugs is the high risk of bleeding complications.

  • Some direct thrombin inhibitors can be used to treat heparin induced thrombocytopenia
  • Pradaxa is an oral, prescription blood-thinning medicine used to reduce the risk of stroke and blood clots in people with atrial fibrillation (AFib) not caused by a heart valve problem
  • Pradaxa does not require routine monitoring
  • There are no blood tests available to monitor the effects of direct thrombin inhibitors
  • This class appears to have a higher risks of bleeding complications than warfarin

Factor Xa Inhibitors: Xarelto (rivaroxaban), Eliquis (apixaban)

Xarelto works by inhibiting one of the clotting factors in the blood. It prevents coagulation by working on Factor Xa. By working on Factor Xa thrombin levels are reduced and the probability of clotting is decreased. Xarelto has been found to be especially useful in people who struggle to maintain a consistent INR. Diet has no effect on Xarelto. Xarelto also does not need to have blood tests done to determine its blood levels. Research has shown that standardized dosing works well with this medication. There are currently no "official" methods to reverse Xarelto but doctors have been using methods such as plasma administration to stop the bleeding and induce coagulation.

  • No blood work
  • Not affected by diet
  • No "official" method of reversal
  • Has been found to be safer for patients who struggle to maintain INR

Heparinoids: Arixtra

Heparinoids are possibly the newest class of anticoagulants. Currently, there is only one drug in this class, Arixtra. Arixtra is a subcutaneous injection that is give once a day. It is usually used short term (only 5-9 days). It is the only anticoagulant that inhibits only factor Xa and does not affect thrombin.

  • Arixtra is typically taken once daily
  • Arixtra is new and therefore may be expensive
  • Arixtra is another anticoagulant option

An IV bag of Heparin by Flippy Rice on Flickr
An IV bag of Heparin by Flippy Rice on Flickr


Heparin is an anticoagulant that works by inhibiting factor Xa and factor IIa, also known as thrombin.  It can be used as an injection or an IV.  Heparin is an older drug and, much like warfarin, has well known dosing and side effects.  Heparin has come under fire in recent years due to recalls.  In each of the recalls heparin was recalled due to contamination.  Heparin is a natural anticoagulant that is made by the body.  Medical heparin comes from the intestinal mucosal tissue of slaughtered pigs and cows.  Heparin has a very short half life (about 1 hour) and therefore must be given in frequent doses or on an IV drip.  Blood levels of heparin must be watched carefully.  As heparin is typically used in hospital settings, the blood testing is not an inconvenience.  

  • Heparin is typically a hospital based medicine
  • Heparin has a short half life (about an hour)
  • Heparin is typically given by IV


Platelets are available in blood to plug damage and holes in the circulatory system. Platelets can stick together when there is a wound and when there is inflamation in the arteries (example: atherosclerosis). Arteries are always under pressure as they have muscular walls. This makes them handle blood differently. For this reason, arterial clots are platelet based. Antiplatelets will be prescribed in situations where the arteries may be to blame for a clot or where the arteries may be at risk for clotting. Some examples are:

  • Stroke
  • TIA (transient ischemic attacks)
  • Atherosclerosis
  • Coronary artery disease
  • Heart attack
  • Angina (chest pain)
  • Peripheral artery disease
  • After angioplasty and stent placement
  • After heart bypass surgery
  • To prevent the formation of blood clots in people with atrial fibrillation

You will note that Factor V Leiden and other clotting disorders are not on this list. Also, pulmonary embolism and deep vein thrombosis (DVT) are absent from this list. This is because antiplatelets are not appropriate therapy for these conditions.

Aspirin by Semarr on Flickr
Aspirin by Semarr on Flickr

Cyclooxygenase inhibitors: aspirin

Aspirin has become an important medication for many people.  Not only does it kill pain, inflamation, and fevers, it also affects platelets. Aspirin blocks the production of thromboxane A-2, a chemical secreted by platelets that helps the platelets to clump.  It does this through it COX-1 inhibition.  Aspirin is the preferred non-steroidal anti inflammatory drug (NSAID) for blood thinning because the other NSAIDs only change the platelet behavior for a short period of time.  Aspirin affects platelets for days rather than mere hours.  Aspirin blocks only one of the pathways that work on platelets.  For this reason, aspirin is a weak anti-platelet medication.  The dose of aspirin that is used depends on the condition that is being treated.  75-150 mg per day is used when aspirin is being used for the long term prevention of strokes and heart attacks.  160-325 ms per days is used for unstable angina and acute heart attacks as the larger dose affects platelets more quickly.  Aspirin can cause side effects.  The primary side effects are centered around gastrointestinal upset and stomach problems.  Sometimes ulcers can occur from aspirin use.  Like other blood thinners, patients should watch for problems with bleeding.

  • Aspirin is inexpensive
  • Aspirin can help with pain as well as blood thinning
  • Aspirin should not be used with ulcers
  • Although aspirin is over the counter, a doctor should be consulted when using aspirin as a blood thinner

Adenosine diphosphate (ADP) receptor inhibitors: ticlopidine (Ticlid), clopidogrel (Plavix)

This class of antiplatelets contains a very well known medication, Plavix. Plavix is typically taken in one 75 mg dose in the morning. Plavix is used to prevent heart attack and stroke. It may be administered after a heart catheterization if there is concern about plaque breaking loose. Some studies have looked at using Plavix as a migraine preventative. Some studies have reported an increased clotting risk for 90 days after stopping Plavix. For this reason there is some concern about using it for migraine prevention.

  • Does not need regular blood testing
  • Taken once a day
  • May ease migraines
  • May cause increased clotting risk for 90 days after stopping the medication
  • Very common and popular medication

Ticlid is another medication in this drug class. The dose for Ticlid is typically 250 mg two times a day. Because of possible side effects patients need to have blood work done every 2 weeks for the first 3 months of starting this medication. These blood tests will help to detect potentially fatal white blood cell drops, platelet drops, bleeding or clotting problems, or liver problems.

  • Needs blood testing every 2 weeks for the first 3 months
  • May cause serious drops in white blood cells or platelets
  • Is taken twice daily

Phosphodiesterase inhibitors: cilostazol (Pletal)

Pletal (cilostazol) can not be used in any patient with congestive heart failure.  The nice thing about Pletal is that it can be discontinued without the rebound (increase in platelet aggregation) seen in some other antiplatelet medications.  Cilostazol widens arteries that supply blood to the legs. Cilostazol also improves circulation by keeping platelets in the blood from sticking together and clotting.  This antiplatelet is typically used in intermittent claudication and can increase the distances that patients can walk without pain.  Pletal should be taken on an empty stomach.  Patients on Pletal should avoid grapefruit as it can cause serious interactions with this medication.  Cilostazol should not be used during pregnancy.

  • Can be stopped without rebound
  • Used in intermittent claudication
  • Patients should take it on an empty stomach
  • Patients should avoid grapefruit
  • Cilostazol should not be used during pregnancy

Glycoprotein IIB/IIIA inhibitors: abciximab (ReoPro), eptifibatide (Integrilin), tirofiban (Aggrastat), defibrotide

This is a collection of medications that are only given in the hospital. They all require IV administration. They are often given with heparin or aspirin before or after a heart procedure to prevent clots. They are also used in heart attack, stroke, and unstable angina. While on these medications patients must have a number of blood tests to ensure that blood chemistry and all blood counts are within safe levels.

  • Used in the hospital setting
  • Used before or after heart procedures

Adenosine reuptake inhibitors: dipyridamole (Persantine, Aggrenox)

Persantine is dipyridamole by itself.  Aggrenox is the combination of aspirin and dirpyridamole.  Aspirin and dirpyridamole are more effective when taken together in a pill than they are if taken as separate pills.  Dipyridamole prevents platelets, blood cells, and blood vessels from using adenosine.  Adenosine is one of the chemicals that the body uses to assist in clot formation.  Dipyridamole also causes vasodilation.  This opens up the blood vessels so there is more space for the blood to flow freely.  Dipyridamole can cause increased headaches when it is first prescribed.  In time the headaches tend to lessen.  Over the counter treatments can help with the headaches until that side effect lessens.  Dipyridamole is considered one of the best treatments to prevent a recurrent stroke in a patient who has already had a stroke.

  • May cause increased headaches at treatment onset
  • Sometimes combined with aspirin in a single pill
  • A strong treatment for preventing recurrent strokes


Thrombolytics are a class of drugs that break up clots that already have formed. This is the only class that is able to dissolved blood clots. Thrombolytics do not prevent clots from occurring.  If a person has a stroke and is immediately rushed to the emergency room thrombolytics can be administered to resolve the stroke quickly.  Patients who are able to use this treatment frequently have less damage from the stroke.  Thrombolytics can also be used when a patient has a pulmonary embolism.  The clot busting medication can dissolve the clots in the lungs and allow oxygen to once again reach the blood stream.  This is the best course for a highly unstable patient with known pulmonary embolism or recent history of deep vein thrombosis.  Work is also being done with deep vein thrombosis itself.  Researchers are using small amounts of thrombolytics on DVT clots in order to dissolve the clot before it causes permanent damage to the vein.  The problem with thrombolytics is that they have a very high risk of bleeding.  They should be used very carefully.  With DVT it is necessary to be able to administer this drug just on the clot itself so that the patient is not put at risk of a serious bleeding incident.  Care should also be taken when selecting patients with pulmonary embolism or stroke.  The cost benefit analysis must be carefully considered.

  • Can be used at stroke onset to limit brain damage
  • Can be used to open up lungs in unstable pulmonary embolism
  • Can be used to prevent damage from deep vein thrombosis
  • Must be used with caution to prevent severe and potentially deadly bleeding
  • Only used in hospital settings due to risks of bleeding

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Comments 15 comments

Anne 6 years ago

My husband has recently experienced a heart attack and our doctor prescribed Plavix. I am not a big fan of drugs, are there any alternatives methods?

allie 6 years ago

good stuff!

musharraf imam, Anaesthetist 5 years ago

A comprehensive and to the point article, must be appreciated.

Sung Hwang 4 years ago

What a great presentation. I have one question though. So, had doctors been prescribing heparin and coumadin way too much for preventing and treating arterial clots like stroke, afib, TIA? Should they have used more antiplatelets much more?

Lwelch profile image

Lwelch 4 years ago from USA Author

With afib blood clots because it pools in the heart. This would indicate warfarin and other anticoagulants in that family. For stroke and TIA what I know is that studies show warfarin etc to be highly effective. Increased risk for TIA and stroke are raised when one has a condition that affects thrombin like factor v Leiden. This shows that platelets are only one part of the story. Platelets are definitely still involved in these conditions. Many patients with stroke or TIA are on both anticoagulants and antiplatelets.

It would be interesting to see a doctor or pharmacist comment to see how the medical community thinks about your question.

Sung Hwang 4 years ago

From reading this article and viewing the video clips, I got the impression that antiplatelet meds do nothing for venous clots, and anticoagulants has SOME benefits treating arterial clots, but not much. In fact, that is almost word for word what the guy in the first two video clips said. Yet anticoagulants are a big part of almost all arterial clot management. That is why I questioned whether or not anticoagulants were being used too much for afib, stroke TIA, etc.

Lwelch profile image

Lwelch 4 years ago from USA Author

You are right. I have thought that question over myself. Afib has the easy answer. Any time blood pools it tends to clot and that is the type of clots that anticoagulants prevent. Tia and stroke are more difficult. As I mentioned, I know that conditions that impact the thrombin system (the system that anticoagulation impacts) up the risk of strokes and TIA. Typically, the lungs filter out any clots from the venous system before they reach the brain. This is how pulmonary embolism occurs. In people who have a patent foramen ovale, hole in the heart, venous clots can reach the brain by passing through the heart.

I really have no more explanation other than you may be right but that studies seem to say anticoagulants help. My guess is that I don't know enough to explain warfarin and TIA and stroke. I am not a doctor.

I am very intrigued by your question and I really would love to see a pharmacist or doctor tackle the answer. I am hoping one stops by and posts.

Patrick 4 years ago

Very informative! Thanks for clarifying the different modalities used for two very different issues.

mysnav 4 years ago

Thank you for your explanation! I finally understand! Hallelujah!

Arun 3 years ago

Very informative on anticoagualants...

Lina 3 years ago

A great informative article !!!!!

My question is in cases where you have a history of DVT ( best treated with anticoagulant ..basically warfarin) , as well as a recent heart attack and stent implantation ( best treated with Plavix and aspirin)..( my brother's case) . Does this patient end up administering 3 blood thinners?? Isn't this too risky??

Lwelch profile image

Lwelch 3 years ago from USA Author

Wow. I don't know the answer to that. I feel like I have heard of people on more thanks one. Aspirin, warfarin, and plavix I believe may be used in pairs. Maybe a medical professional will stop in and shed some light on this.

mohamed galal 18 months ago


Rasha 14 months ago

Great article ;)

Lwelch profile image

Lwelch 14 months ago from USA Author


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