“Blood thinner” is an informal term. These medications do not literally dilute the blood — they reduce the body's ability to form harmful clots or prevent existing clots from becoming larger. There are two main categories, anticoagulants and antiplatelet medications, and although both are commonly called blood thinners, they work differently and may be prescribed for different medical conditions.
What Are Anticoagulants?
Anticoagulants interfere with proteins involved in the blood-clotting process.
Common examples include:
- Warfarin
- Apixaban
- Rivaroxaban
- Dabigatran
- Edoxaban
- Enoxaparin
- Heparin
They may be prescribed for conditions such as:
- Atrial fibrillation
- Deep-vein thrombosis
- Pulmonary embolism
- Certain heart-valve conditions
- Prevention of clots after selected surgeries
- Other conditions that increase the risk of harmful blood clots
What Are Antiplatelet Medications?
Platelets are small components of the blood that stick together to help form clots.
Antiplatelet medications reduce platelet activation or prevent platelets from sticking together as easily.
Common examples include:
- Aspirin
- Clopidogrel
- Prasugrel
- Ticagrelor
They may be prescribed after:
- A heart attack
- Certain types of stroke
- Coronary stent placement
- Other cardiovascular procedures
Anticoagulants and antiplatelet medications are not interchangeable. The appropriate medication depends on the type of clotting risk being treated.
Is Aspirin Safe for Everyone?
No.
Aspirin is available without a prescription, but daily aspirin therapy can increase the risk of bleeding.
Do not begin taking aspirin every day to prevent a heart attack or stroke without speaking with a qualified healthcare professional.
Whether aspirin is appropriate depends on factors such as:
- Age
- Previous heart attack or stroke
- Bleeding risk
- Stomach-ulcer history
- Other medications
- Cardiovascular risk
- Kidney or liver disease
A medication being sold over the counter does not make it appropriate for every patient.
What Is Different About Warfarin?
Warfarin requires regular blood testing using the international normalized ratio, commonly called the INR.
The INR helps determine whether the dose is producing the intended anticoagulant effect.
If the INR is too low, the medication may not provide enough protection against blood clots. If it is too high, the risk of bleeding may increase.
The warfarin dose may be adjusted based on:
- INR results
- Diet
- Illness
- Other medications
- Antibiotic use
- Alcohol intake
- Changes in health status
Vitamin K can affect warfarin. Patients generally do not need to eliminate foods containing vitamin K, but they should try to keep their intake reasonably consistent.2
Foods containing vitamin K include:
- Spinach
- Kale
- Collard greens
- Broccoli
- Brussels sprouts
- Other leafy green vegetables
Large or sudden changes in diet can affect anticoagulation control.
Do All Blood Thinners Require INR Testing?
No.
Direct oral anticoagulants such as apixaban, rivaroxaban, dabigatran, and edoxaban do not usually require routine INR monitoring.
However, patients may still need periodic monitoring of:
- Kidney function
- Liver function
- Blood counts
- Signs of bleeding
- Medication adherence
- Drug interactions
The absence of routine INR testing does not mean the medication requires no monitoring.
What Are Signs of Excessive Bleeding?
Contact a healthcare professional promptly for symptoms such as:
- Frequent nosebleeds
- Bleeding gums
- Unusually heavy menstrual bleeding
- Large or unexplained bruises
- Blood in the urine
- Red or black stools
- Vomiting blood
- Persistent bleeding from a cut
- Unusual weakness or fatigue
Seek emergency medical attention for:
- A serious fall or head injury
- Sudden, severe headache
- New weakness or numbness
- Difficulty speaking
- Uncontrolled bleeding
- Coughing or vomiting significant amounts of blood
- Fainting
- Severe confusion
- Loss of consciousness
Bleeding inside the body is not always visible. New neurological symptoms, severe weakness, dizziness, or unexplained pain should not be ignored.1
Which Over-the-Counter Medicines Can Interact?
Some OTC medications can increase bleeding risk or interfere with blood-thinner therapy.
Potential concerns include:
- Ibuprofen
- Naproxen
- Aspirin-containing pain products
- Certain cold and flu medicines
- Bismuth-containing stomach products
- Herbal supplements
- High-dose fish oil supplements
- Products containing multiple active ingredients
Nonsteroidal anti-inflammatory drugs, also known as NSAIDs, may increase the risk of stomach ulcers and bleeding when combined with anticoagulants or antiplatelet medications.
Ask a pharmacist before using an OTC pain reliever.
Can Supplements Interact With Blood Thinners?
Yes.
Herbal and dietary supplements may affect clotting, increase bleeding risk, or change how a blood thinner works.
Potentially concerning supplements may include:
- Ginkgo
- Garlic supplements
- Ginseng
- Turmeric or curcumin
- St. John's wort
- High-dose vitamin E
- High-dose fish oil
The level of risk depends on the specific product, dose, and medication.
Include all supplements on your medication list and discuss them with your pharmacist or prescriber.
What About Dental Work or Surgery?
Tell every dentist, surgeon, and healthcare professional that you take an anticoagulant or antiplatelet medication.
Do not stop the medication independently before a procedure.
Stopping treatment may reduce bleeding risk, but it may also increase the risk of:
- Stroke
- Deep-vein thrombosis
- Pulmonary embolism
- Heart attack
- Stent thrombosis
The prescriber and procedure team should provide a coordinated plan based on the medication, procedure, and reason for treatment.
What If You Miss a Dose?
Missed-dose instructions vary among blood thinners.
Some medications should be taken when remembered within a particular timeframe. Others should be skipped when the next dose is approaching.
Do not double the dose unless a healthcare professional or the medication's official instructions specifically direct you to do so.
Call your pharmacist or prescriber when the instructions are unclear, particularly if you missed more than one dose.
Can Blood Thinners Be Stopped Suddenly?
Stopping an anticoagulant or antiplatelet medication without medical guidance can increase the risk of serious clotting complications.
This may be especially dangerous for patients with:
- Atrial fibrillation
- A recent blood clot
- A coronary stent
- A mechanical heart valve
- A recent heart attack
- A recent stroke
Contact the prescriber promptly when the medication becomes unaffordable, is not covered by insurance, causes side effects, or is unavailable.
Do not simply stop taking it.
Questions to Ask Your Pharmacist
- Why am I taking this medication?
- Is it an anticoagulant or an antiplatelet drug?
- What should I do if I miss a dose?
- Which OTC pain relievers are safe for me?
- Are there foods or supplements I should avoid?
- Do I need laboratory monitoring?
- What signs of bleeding require urgent care?
- What should I do before dental work or surgery?
- Does this medication interact with my other prescriptions?
- Should I carry a medication identification card?
The Bottom Line
Blood thinners help prevent dangerous clots, but they can also make bleeding more difficult to stop. Patients should know the name of the medication, why it was prescribed, how and when to take it, what monitoring it requires, which medicines and supplements may interact, what signs of bleeding require medical attention, and whom to contact before surgery or dental procedures.
Frequently Asked Questions
What's the difference between an anticoagulant and an antiplatelet medication?
Anticoagulants like warfarin and apixaban interfere with clotting proteins, while antiplatelets like aspirin and clopidogrel reduce platelet activation. They're prescribed for different clotting risks and are not interchangeable.
Can I take ibuprofen while on a blood thinner?
NSAIDs like ibuprofen and naproxen may increase the risk of stomach ulcers and bleeding when combined with anticoagulants or antiplatelet medications. Ask a pharmacist before using any OTC pain reliever.
Do I need to avoid green leafy vegetables on warfarin?
No. You generally don't need to eliminate vitamin K-containing foods like spinach and kale — the key is keeping your intake reasonably consistent, since large or sudden changes can affect your INR.
Can I stop my blood thinner before dental work on my own?
No. Tell your dentist or surgeon you take an anticoagulant or antiplatelet medication, but don't stop it independently — stopping without a coordinated plan can increase the risk of stroke, clot, or stent complications.
A blood thinner should never become an anonymous tablet in a pillbox. Know whether you take an anticoagulant or an antiplatelet medication, why you need it, and what to do when a dose is missed or a procedure is planned.
References
- MedlinePlus, National Library of Medicine, NIH. Taking Warfarin. medlineplus.gov/ency/patientinstructions/000292.htm
- MedlinePlus, National Library of Medicine, NIH. Vitamin K. medlineplus.gov/ency/article/002407.htm