When not to use anticoagulants? A guide to risks and contraindications

October 11, 2025 •

5 min read

According to studies, bleeding is the most feared complication of oral anticoagulants and is associated with a high case-fatality rate, particularly intracranial hemorrhage. Therefore, understanding when not to use anticoagulants is critical for patient safety and effective care planning.

Quick Summary

This article explores the absolute and relative contraindications for anticoagulant therapy, detailing scenarios such as active bleeding, recent surgery, and severe organ dysfunction. It explains how to weigh the benefits of preventing thrombosis against the risks of hemorrhage in specific patient populations, emphasizing individualized decision-making.

Key Points

Absolute Contraindications: Certain conditions, including major active bleeding, recent intracranial hemorrhage, and severe bleeding disorders, make anticoagulant use prohibitively dangerous.
Relative Contraindications: For situations like moderate-to-severe liver or renal disease, or uncontrolled hypertension, the decision to use anticoagulants requires a careful, individualized risk-benefit analysis.
Drug-Specific Considerations: Different anticoagulants, such as Warfarin (VKA) and DOACs (like Apixaban or Rivaroxaban), have distinct contraindications related to pregnancy, liver function, and renal clearance.
High-Risk Patient Populations: Elderly patients with a high risk of falls and patients with traumatic brain injury require careful evaluation, balancing the risk of thrombotic events against the danger of hemorrhage.
Modifying Risk Factors: Before and during anticoagulant therapy, it is crucial to manage modifiable bleeding risk factors, such as controlling blood pressure and avoiding concomitant medications like NSAIDs.
Individualized Decision-Making: The decision of when not to use anticoagulants must be a collaborative one, involving a thorough discussion between the patient, their family, and their healthcare team.

Anticoagulants are vital medications for preventing and treating dangerous blood clots associated with conditions like atrial fibrillation, deep vein thrombosis (DVT), and pulmonary embolism (PE). However, their use involves a significant risk of bleeding. Recognizing when this risk outweighs the benefit of preventing blood clots is crucial for patient safety. This guide covers contraindications and high-risk scenarios for anticoagulant use, including vitamin K antagonists (VKAs) like warfarin and direct oral anticoagulants (DOACs) such as apixaban, rivaroxaban, and dabigatran.

Absolute Contraindications

Absolute contraindications mean anticoagulants should almost never be used due to a very high risk of severe bleeding.

Major Active Bleeding

Patients with major or life-threatening bleeding, such as severe bleeding in the stomach, intestines, or brain, should not receive anticoagulants. Managing the bleeding is the immediate priority. Anticoagulation may be considered later for conditions like GI bleeding after the source is treated.

Recent Intracranial Hemorrhage

Intracranial hemorrhage (ICH) is a very serious complication of anticoagulant use with a high mortality rate. The risk of the bleeding worsening is high in the beginning, making anticoagulants absolutely contraindicated. Deciding to restart therapy later is complex and balances the risk of more bleeding against the risk of blood clots.

Severe Bleeding Disorders

Individuals with severe inherited or acquired bleeding disorders, such as hemophilia or very low platelet counts, should not be given anticoagulants. For mild bleeding disorders, the decision is made on a case-by-case basis with expert input.

Recent Major Surgery

Using anticoagulants right after major surgery, particularly on the brain, spine, or eyes, is usually contraindicated because of the high risk of severe bleeding. When to resume therapy depends on the surgery type and bleeding risk.

Severe Uncontrolled Hypertension

Very high and uncontrolled blood pressure significantly increases the risk of ICH, which is made worse by anticoagulants. Therefore, anticoagulation is not recommended until blood pressure is properly managed.

Relative Contraindications and Cautionary Scenarios

Relative contraindications mean the risks and benefits must be carefully considered. Anticoagulants might still be used, but with close monitoring and managing any other risk factors.

End-Stage Liver Disease (Child-Pugh C)

Severe liver impairment (Child-Pugh C) increases the risk of bleeding and is a contraindication for DOACs. While warfarin can be an option in these patients, it requires very careful management.

High Fall Risk in Elderly Patients

Older age and frequent falls increase the risk of traumatic bleeding, especially ICH. While preventing stroke often remains the priority, the decision for elderly patients at high risk of falls is individualized and involves discussing the risks and benefits.

Moderate-to-Severe Renal Impairment

Kidney function is important for DOACs as many are removed from the body by the kidneys. Severe kidney problems can lead to higher drug levels and increased bleeding risk, requiring dose adjustments or making certain DOACs unsuitable. Dabigatran is generally not used in severe renal impairment, and other DOACs like apixaban may need dose changes.

Concurrent Medications

Taking other medications that affect blood clotting can significantly increase bleeding risk. This includes drugs like aspirin, NSAIDs, certain antibiotics, and some herbal supplements. A careful review of all medications is essential.

Anticoagulant Use in Specific Patient Populations

Pregnancy and Anticoagulants

Warfarin is generally not used during pregnancy, particularly in the first trimester, due to the risk of birth defects. It is sometimes used for women with mechanical heart valves when the benefits are deemed to outweigh the risks. Low molecular weight heparins (LMWH) are considered safer in pregnancy as they don't cross the placenta. DOACs are not recommended during pregnancy due to limited safety data.

Anticoagulation following Traumatic Brain Injury (TBI)

Deciding whether to restart anticoagulation after a traumatic brain injury (TBI), especially with associated ICH, is challenging. While stopping therapy reduces the risk of more bleeding, it increases the risk of dangerous blood clots. For most patients, restarting anticoagulation is linked to better outcomes despite the bleeding risk. The best time to resume therapy is often debated.

Comparison of VKA vs. DOAC Contraindications


Feature	Vitamin K Antagonists (Warfarin)	Direct Oral Anticoagulants (DOACs)
Monitoring	Requires frequent blood tests (INR) to stay in the right range, which can be difficult with diet changes or other health issues.	Doesn't usually require routine blood tests for monitoring.
Reversal Agents	Can be reversed with Vitamin K or certain blood products, but can be slow.	Specific and fast-acting reversal agents are available for some DOACs.
Pregnancy	Avoided in pregnancy due to risk of birth defects, except in very specific cases like mechanical heart valves.	Not recommended during pregnancy because safety for the baby is not known.
Severe Renal Impairment	Not removed by the kidneys, so can be used cautiously in severe kidney disease, although dosing can be tricky.	How the kidneys remove the drug varies. Severe kidney problems require dose reduction or mean certain DOACs cannot be used.
Severe Liver Disease	Can sometimes be used cautiously in severe liver disease (Child-Pugh C), but management is difficult.	Cannot be used in severe liver disease (Child-Pugh C), and some are not used in moderate liver disease (Child-Pugh B).
Drug Interactions	Highly affected by food (Vitamin K) and many other medications due to how it's processed in the body.	Fewer interactions than warfarin, but still possible with some medications that affect certain enzymes or transporters.

Shared Decision-Making and Modifying Risks

When a patient has risk factors that are relative contraindications, the decision to use anticoagulation should involve the doctor, patient, and family. This discussion should cover the patient's risk of blood clots versus bleeding, their overall health, lifestyle, and preferences. Reducing modifiable bleeding risk factors is also key. Important strategies include:

Controlling blood pressure: This is very effective in lowering the risk of ICH.
Managing medications: Avoiding or minimizing other medications that increase bleeding risk, such as NSAIDs.
Regular checks: For warfarin users, keeping the INR stable is vital. For DOAC users, checking kidney and liver function regularly is important.
Patient education: Patients and caregivers need to know the signs of bleeding and when to get medical help.

Conclusion

Anticoagulants are essential for preventing and treating dangerous blood clots, but they carry a significant bleeding risk. Knowing when not to use anticoagulants is crucial for safe medical practice. Absolute contraindications like major active bleeding or recent intracranial hemorrhage make anticoagulants unsafe. Relative contraindications, such as advanced liver or kidney disease, uncontrolled high blood pressure, and high fall risk, require a careful, individualized assessment of risks and benefits. The choice of anticoagulant (VKA or DOAC) also depends on these patient factors. By evaluating these risks, managing modifiable factors, and involving patients in decisions, healthcare providers can improve outcomes and reduce bleeding complications.

Managing Anticoagulation in High-Risk Populations

Frequently Asked Questions

Warfarin is contraindicated during pregnancy, particularly the first trimester, due to the risk of congenital disabilities. Its use is only considered for specific high-risk conditions like mechanical heart valves where the benefit outweighs the risk. Low molecular weight heparins are a safer alternative. Direct oral anticoagulants (DOACs) are generally not recommended due to a lack of safety data.

Yes, but the decision to restart anticoagulation after a major bleeding event, such as a gastrointestinal bleed or intracranial hemorrhage, is complex and requires careful assessment of individual risk factors. The timing varies based on the bleed's location and severity, but studies suggest that for many patients, the benefits of resuming therapy outweigh the risks after the acute phase has been managed.

Intracranial hemorrhage (ICH) is the most severe and life-threatening complication of anticoagulant therapy. The risk is significantly increased in patients with uncontrolled hypertension, recent head trauma, or certain vascular malformations. DOACs generally have a lower risk of ICH compared to warfarin.

No, but they should be used with extreme caution. The use of DOACs is contraindicated in patients with severe liver disease (Child-Pugh C). Some DOACs, like rivaroxaban, are also contraindicated in moderate liver disease (Child-Pugh B). Warfarin use is possible but challenging to manage in patients with liver impairment.

Not necessarily. While advanced age and a history of falls increase the risk of bleeding, especially intracranial hemorrhage, the risk of stroke in patients with conditions like atrial fibrillation often outweighs this risk. The decision must be made on an individual basis, carefully considering the patient's specific risks and benefits.

Certain medications and supplements can increase the risk of bleeding when taken with anticoagulants. These include NSAIDs, aspirin, certain antibiotics, and herbal remedies like St. John's Wort. All concomitant medications should be reviewed by a healthcare provider before starting or changing anticoagulant therapy.

DOACs are generally associated with a lower risk of overall major bleeding and a significantly lower risk of intracranial hemorrhage compared to warfarin. However, some DOACs have been linked to a higher risk of gastrointestinal bleeding. The bleeding profile also varies between different DOACs, with apixaban potentially having a better GI safety profile compared to rivaroxaban.