What medication not to take while on blood thinners?

October 11, 2025 •

4 min read

According to the Cleveland Clinic, taking certain herbal supplements while on blood thinners could do more harm than good. Knowing what medication not to take while on blood thinners is essential for preventing dangerous drug interactions and avoiding potentially life-threatening bleeding episodes.

Quick Summary

This guide outlines the specific prescription drugs, over-the-counter medications, and herbal supplements that interact with blood thinners, significantly increasing the risk of bleeding. Learn to identify and avoid common combinations to ensure your safety.

Key Points

Avoid NSAIDs: Never take NSAIDs like ibuprofen, naproxen, or aspirin for pain relief without a doctor's approval, as they significantly increase bleeding risk.
Check OTC Labels: Read the labels of all over-the-counter medications, including cold remedies and stomach aids, for hidden NSAIDs and salicylates.
Be Wary of Supplements: Inform your doctor about all herbal and dietary supplements, as many like ginkgo, garlic, and fish oil can interact with blood thinners.
Manage Warfarin with Caution: For those on warfarin, be aware that antibiotics, antifungals, and changes in vitamin K intake can destabilize your INR.
Communicate with Providers: Always inform your doctors, pharmacists, and dentists about your blood thinner use before starting new medications or undergoing procedures.

The Critical Risk of Drug-Induced Bleeding

Blood thinners, also known as anticoagulants, are powerful medications prescribed to prevent and treat dangerous blood clots that can cause strokes, heart attacks, and pulmonary embolisms. They work by interfering with the body's natural clotting process. However, this life-saving function also creates a heightened risk of bleeding, and this risk is significantly amplified when combined with other substances that also affect blood clotting. Taking a new medication, including common over-the-counter (OTC) products and natural supplements, without consulting a healthcare provider can turn a minor interaction into a medical emergency. The consequences range from an inconvenient increase in bruising to severe, life-threatening internal hemorrhaging. Understanding the classes of drugs and supplements to avoid is the first and most critical step toward medication safety.

Over-the-Counter (OTC) Medications to Avoid

Many seemingly harmless OTC products can be extremely dangerous when mixed with blood thinners. The most common culprits are pain relievers that act as nonsteroidal anti-inflammatory drugs (NSAIDs).

NSAIDs and Their Hidden Danger

Aspirin: A prime example of an NSAID, aspirin is often used for its pain-relieving and fever-reducing properties. At low doses, it is also prescribed as an antiplatelet agent. However, combining aspirin with another blood thinner, especially without a doctor's explicit recommendation, drastically increases the risk of both minor and major bleeding. For many patients, the potential harm far outweighs the benefit.
Ibuprofen (Advil, Motrin) and Naproxen (Aleve): These are standard NSAIDs that can significantly raise your risk of bleeding. They also cause damage to the protective lining of the stomach and digestive tract, creating potential sites for bleeding. Many common cold, sinus, and sleep-aid medications also contain NSAIDs, so reading labels carefully is vital.
Bismuth Subsalicylate (Pepto-Bismol, Kaopectate): This medication is used to treat upset stomachs and diarrhea. It contains salicylates, a component similar to aspirin, which can interfere with blood clotting and should be avoided.

Prescription Medications That Require Caution

Many prescription drugs, while not explicitly blood thinners themselves, can interfere with their metabolism or affect platelet function. Always inform every doctor and pharmacist about all medications you are taking.

Antibiotics and Antifungals

Certain antibiotics can increase the effect of blood thinners like warfarin, significantly raising your International Normalized Ratio (INR) and bleeding risk. Some common examples of interacting medications include:

Ciprofloxacin (Cipro)
Metronidazole (Flagyl)
Sulfamethoxazole / Trimethoprim (Bactrim)

Similarly, some antifungal medications can increase the concentration of blood thinners in the blood. Patients on warfarin should be especially cautious with antifungals such as fluconazole (Diflucan).

Antidepressants

Selective serotonin reuptake inhibitors (SSRIs), a common class of antidepressants, can independently increase the risk of bleeding. When taken alongside a blood thinner, this risk can be compounded. Examples of SSRIs that warrant careful monitoring include:

Sertraline (Zoloft)
Fluoxetine (Prozac)
Paroxetine (Paxil)

Anticonvulsants

Some anti-seizure medications can either decrease or increase the effect of blood thinners, potentially pushing your INR out of a safe range. Carbamazepine (Tegretol) and Phenytoin (Dilantin) are examples of anticonvulsants that can affect warfarin metabolism.

Herbal and Dietary Supplements

The notion that “natural” supplements are inherently safe is a misconception. Many herbs and vitamins can have a significant effect on blood clotting.

Ginkgo Biloba, Garlic, Ginseng, Turmeric, Fish Oil: These popular supplements are known for their natural anti-platelet or anti-coagulant effects. Combining them with a prescription blood thinner can have a dangerous additive effect, dramatically increasing bleeding risk.
St. John's Wort: This herbal supplement can decrease the effectiveness of certain blood thinners, potentially reducing their therapeutic benefit and raising the risk of clot formation.
Vitamin E: High doses of vitamin E can increase the blood-thinning effect of other medications.
High-Vitamin K Supplements and Foods: For individuals on warfarin, a consistent daily intake of vitamin K is vital for maintaining a stable INR. High-dose vitamin K supplements or significant, sudden increases in vitamin K-rich foods (e.g., leafy greens) can counteract warfarin's effect.

Comparison Table: Pain Relievers and Blood Thinners


Pain Reliever Type	Examples	Risk with Blood Thinners	Recommended Action
NSAIDs	Ibuprofen (Advil), Naproxen (Aleve), Aspirin	Significantly increases bleeding risk and gastrointestinal irritation.	Avoid completely, unless specifically instructed by a doctor.
Acetaminophen	Tylenol (at low doses)	Generally considered safer, but high or prolonged doses can increase warfarin's effect.	Use lowest effective dose for shortest duration; consult a doctor for prolonged use.
OTC Stomach Aids	Pepto-Bismol, Alka-Seltzer	Contain salicylates, which act like aspirin and increase bleeding risk.	Avoid, and discuss safe alternatives with a doctor.
Strong Painkillers	Tramadol	Can affect blood thinners, increasing bleeding risk.	Avoid or use with extreme caution under a doctor's supervision.

Special Considerations for All Blood Thinners

Beyond specific medication interactions, other lifestyle factors and habits can pose risks. Here are some essential guidelines for anyone taking blood thinners:

Always inform all healthcare providers, including dentists, surgeons, and pharmacists, that you are on a blood thinner before any procedure or new prescription.
Be cautious with alcohol consumption. Excessive alcohol can affect how quickly your blood clots.
For those on warfarin, a consistent, rather than variable, intake of vitamin K-rich foods is recommended. Consult with your doctor or dietitian.
Be aware of the contents of your supplements. Proprietary blends often hide interacting ingredients.

Conclusion: Navigating Medications Safely

Taking blood thinners is a critical part of managing a medical condition, but it requires a high degree of vigilance to remain safe. The number of potentially harmful drug and supplement interactions is extensive and can have serious consequences. The safest approach is to assume any new medication, vitamin, or herbal supplement could be dangerous until you confirm its safety with your healthcare provider. This proactive communication is the most effective way to prevent dangerous drug interactions and protect your health while on blood thinners.

Visit the Cleveland Clinic for more tips on staying safe while taking blood thinners.

Frequently Asked Questions

Acetaminophen is generally considered a safer option for pain and fever, especially compared to NSAIDs. However, taking high doses or using it for a prolonged period, particularly with warfarin, can still increase bleeding risk. Always use the lowest effective dose for the shortest time possible and consult your doctor.

NSAIDs increase bleeding risk by interfering with platelet function and, crucially, by damaging the protective lining of the gastrointestinal tract. This creates a higher potential for internal bleeding, especially when combined with the anticoagulant effect of blood thinners.

Excessive alcohol consumption can affect how quickly your blood clots and can increase your chances of falling and injuring yourself. It is best to discuss your alcohol use with your doctor, as moderate intake may be permissible depending on your overall health.

No. While some interactions are common, such as with NSAIDs and supplements, older anticoagulants like warfarin have different and often more numerous interactions with foods and medications than newer blood thinners (DOACs like Eliquis or Xarelto). Always check with your healthcare provider for specific advice.

Many supplements have natural blood-thinning effects and should be avoided or used with caution. These include ginkgo biloba, garlic, ginseng, turmeric, fish oil, and high-dose vitamin E.

Contact your doctor or a pharmacist immediately for guidance. Be aware of any symptoms of increased bleeding, such as unusual bruising, blood in your urine or stool, or persistent nosebleeds.

Many multi-symptom cold and flu products contain NSAIDs like ibuprofen or aspirin. Check the 'Active Ingredients' list on the packaging for any NSAIDs or salicylates. Opt for products that contain only acetaminophen, but again, use caution and consult a healthcare provider for any concerns.