Anticoagulants are a family of medications that stop your blood from clotting too easily. They can break down existing clots or prevent clots from forming in the first place. These medications can help stop life-threatening conditions like strokes, heart attacks and pulmonary embolisms, all of which can happen because of blood clots.
Anticoagulants are a group of medications that decrease your blood’s ability to clot. They do that by letting your body break down existing clots or by preventing new clots from forming.
Anticoagulants come in many different forms, including injections, intravenous (IV) drugs, and medications you take by mouth. They often treat and prevent life-threatening conditions that can happen because of blood clots, like strokes, heart attacks and pulmonary embolisms.
When blood clots work like they’re supposed to, they form at the site of an injury that needs repair and they stay put. However, when clots don't stay in one place or form in your bloodstream, they can be extremely dangerous. If a clot is too large, it can get stuck in a smaller blood vessel. If that smaller blood vessel is in a critical location, it can block blood flow that one of your organs needs to survive.
Blockages from blood clots can cause the following deadly events:
Anticoagulants can protect individuals who have a condition or disease that could cause them to have any of the above clot-related events.
Some of those conditions include:
Anticoagulants are commonly prescribed medications. This is especially true thanks to the approval of several newer drugs, which you take by mouth, within the past 10 years. In the United States, more than 5 million individuals covered by Medicare Part D received a prescription for an anticoagulant medication in 2019. In addition, about one-third of all hospital patients receive some form of anticoagulant medication.
Your body is constantly balancing clotting and anti-clotting processes. If your blood doesn't clot enough, an injury can cause severe blood loss or even death. If it clots too much, it can cause the dangerous medical events mentioned above. Certain blood components keep your clotting processes in an inactive state. That way, your body can activate them quickly when you have an injury that needs repair.
Thanks to that balancing act, clotting is usually a helpful process. It stops bleeding, creates a protective covering to keep germs and debris out of a wound, and then rebuilds the skin so it’s good as new (or nearly so, if the wound leaves a scar).
Anticoagulants work by interfering with the normal clotting processes. Just like their name suggests, they prevent or undo coagulation, the process where your blood solidifies to form a clot. Depending on the type of anticoagulant, the clotting process disruption happens in different ways.
Heparin and its derivatives
Heparin is a medication that inhibits clotting by activating your body's anti-clotting processes. One of the anticlotting processes uses a type of blood protein called antithrombin. Heparin works by activating antithrombin, and then antithrombin keeps other parts of the clotting process from working normally.
Heparin comes in two different types, and there is a third medication that is closely related:
Direct thrombin inhibitors
Thrombin inhibitors work by attaching to thrombin, keeping it from assisting clotting processes. They are often used as alternatives to heparin and its variants, especially to prevent the formation of clots after certain medical procedures. These include argatroban, desirudin and bivalirudin.
Warfarin (vitamin K antagonist)
Warfarin is a vitamin K antagonist, meaning it blocks the use of vitamin K — a key ingredient in the clotting process. However, a major drawback of warfarin is that it needs careful dosing and regular lab testing to prevent complications. When the dosage isn’t precise enough, it can lead to severe bleeding.
In some cases, certain conditions mean that warfarin is the only anticoagulant that you can take. These include:
Direct oral anticoagulants
These medications can all be taken regularly without regular lab testing and are often used when warfarin isn’t an option. One medication, dabigatran, is a thrombin inhibitor similar to the IV thrombin inhibitors listed earlier. Other medications, apixaban, edoxaban and betrixaban, are all inhibitors of factor Xa (10-A), a key clotting component.
Anticoagulants are extremely effective in preventing life-threatening conditions like stroke, pulmonary embolism and heart attack. There are also several different ways that these medications work. That means people who can’t take one medication may still be able to take a similar medication.
The most common side effect risk with any anticoagulant is bleeding. Depending on the medication used, other potential risks exist.
Warfarin has a much higher risk of causing bleeding because the dosage must be precise. Other risks and side effects include:
Heparin can affect other components of your blood and your bones, with side effects ranging from mild to severe.
Heparin-induced thrombocytopenia (throm-bo-sigh-toe-pee-knee-uh), often abbreviated as HIT, has two forms:
HIT has a very high rate of causing severe or permanent complications. Because of that, platelet level monitoring is very important for anyone who’s receiving unfractionated or low-molecular-weight heparin. If a healthcare provider suspects HIT, they will immediately stop giving you heparin (in either of those two forms) and switch to another medication.
This complication is usually only seen with long-term use of heparin (more than one month). It happens because heparin decreases the formation of new bone cells and increases the rate at which old bone cells are naturally broken down by your body. It’s less likely to happen with LMWH heparin.
Direct oral anticoagulants can sometimes cause indigestion or bleeding in your gastrointestinal tract.
In general, your healthcare provider is the person who can best explain any possible reasons you shouldn’t take anticoagulant medications. You should ask your healthcare provider if you shouldn’t take anticoagulants because of any other medications you take or conditions you have.
There are several conditions that mean you shouldn’t take any kind of anticoagulant (these conditions are called absolute contraindications). Some of these include:
Relative contraindications are conditions where anticoagulant use should be considered on a case-by-case basis. These include:
Several conditions might keep you from taking certain anticoagulants. These conditions, listed by medication, include:
How long you can take an anticoagulant depends on which medication you take and how you take it. Most IV and injectable anticoagulants aren’t meant for long-term use.
However, you can take many oral anticoagulants for longer periods. Depending on which one your healthcare provider prescribes, you may be able to take it indefinitely.
You should call your doctor if you have any symptoms of moderate to severe bleeding. These include:
People who take blood thinners are also at risk for severe bleeding — especially internal bleeding —when they’re injured. You should get immediate medical care if you have any of the following symptoms:
A note from Cleveland Clinic
Anticoagulants are a group of medications that see widespread use for a variety of reasons. They help prevent and treat clot-based health conditions like stroke and pulmonary embolism. These medications have life-saving potential. While they're extremely helpful, they also increase your risk of bleeding, so it’s important to talk with your healthcare provider about how to avoid severe bleeding if you’re injured.
Last reviewed by a Cleveland Clinic medical professional on 01/10/2022.
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