What medication can you not take when on blood thinners?

October 10, 2025 •

4 min read

Anticoagulants are among the most common medications that cause adverse drug events in hospitalized patients [1.10.2]. When taking these vital medications, it is crucial to understand the answer to the question, 'What medication can you not take when on blood thinners?' to avoid dangerous interactions.

Quick Summary

Taking blood thinners requires caution with other drugs. Many over-the-counter pain relievers (NSAIDs), certain antibiotics, antifungals, antidepressants, and herbal supplements can dangerously increase bleeding risk.

Key Points

NSAIDs Are High-Risk: Never take NSAIDs like ibuprofen or naproxen with blood thinners without a doctor's approval due to a high risk of stomach bleeding [1.2.5, 1.6.1].
Check OTC Cold & Pain Meds: Many combination over-the-counter products for colds, pain, and sleep contain hidden NSAIDs [1.2.5].
Supplements Interact: Herbal supplements like St. John's wort, garlic, and ginkgo biloba can dangerously interfere with blood thinners [1.2.2, 1.5.1].
Antibiotics Change Effects: Certain antibiotics can dramatically increase your bleeding risk, requiring close monitoring or dose adjustments [1.7.1, 1.7.3].
Warfarin and Vitamin K: If you take warfarin, maintain a consistent daily intake of Vitamin K from foods like leafy greens to keep your medication stable [1.9.4].
Antidepressants Increase Risk: SSRI and SNRI antidepressants can increase the likelihood of bleeding when taken with anticoagulants [1.8.1, 1.8.2].
Always Consult a Professional: Before taking any new medication, supplement, or making major dietary changes, consult your doctor or pharmacist [1.2.2].

Understanding Blood Thinners and Interaction Risks

Blood thinners, which include anticoagulants like warfarin and direct oral anticoagulants (DOACs) such as apixaban (Eliquis) and rivaroxaban (Xarelto), are essential for preventing and treating blood clots [1.6.5]. However, their effectiveness can be dangerously altered by other substances. An interaction can either increase the anticoagulant effect, leading to a higher risk of serious bleeding, or decrease it, raising the risk of clotting [1.3.1]. Inpatient adverse drug events related to anticoagulants are often preventable and frequently caused by medication errors [1.10.2]. Therefore, knowing which medications to avoid is a critical part of patient safety.

Over-the-Counter (OTC) Medications: The Hidden Danger

The most significant group of interacting OTC medications is Nonsteroidal Anti-Inflammatory Drugs (NSAIDs) [1.2.5]. These are common pain and fever reducers that many people take without a second thought.

NSAIDs to Avoid: This class includes ibuprofen (Advil, Motrin), naproxen (Aleve), and aspirin [1.3.1, 1.2.5]. Combining NSAIDs with any blood thinner significantly increases the risk of bleeding, especially gastrointestinal bleeding [1.6.1, 1.6.4]. The FDA requires that all OTC products containing NSAIDs include a warning about bleeding risks on their label [1.2.5]. These ingredients can also be found in combination products for colds, headaches, and sleeplessness, such as Advil PM or Alka-Seltzer Plus Cold [1.2.5].
Stomach Medications: Some products for upset stomachs, like Pepto-Bismol and Kaopectate, contain salicylates (an aspirin-like compound) and should be avoided [1.2.5, 1.3.4].
Safer Alternatives: For pain relief, acetaminophen (Tylenol) is generally considered a safer option, though high doses should be avoided, particularly with warfarin [1.6.4, 1.3.2].

Prescription Medication Interactions

Numerous prescription drugs can interfere with blood thinners. It is vital that all your prescribing doctors are aware you are on an anticoagulant.

Antibiotics and Antifungals: Many antibiotics can significantly alter the effect of blood thinners, often very quickly [1.3.1]. For example, drugs like trimethoprim/sulfamethoxazole, ciprofloxacin, levofloxacin, clarithromycin, and metronidazole can increase warfarin's effect [1.7.1, 1.7.3]. Antifungals like fluconazole (Diflucan) and ketoconazole also increase bleeding risk [1.2.2, 1.4.3]. Conversely, rifampin can decrease a blood thinner's effectiveness, increasing clot risk [1.4.3, 1.7.4].
Antidepressants: Selective Serotonin Reuptake Inhibitors (SSRIs) such as fluoxetine (Prozac) and sertraline (Zoloft), as well as Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs), can impair platelet function and increase bleeding risk when combined with anticoagulants [1.2.4, 1.8.3]. Studies show this combination is associated with a 33% increased risk of major bleeding [1.8.1, 1.8.4].
Other Cardiovascular Drugs: Medications like amiodarone, used for irregular heart rhythms, can inhibit the metabolism of warfarin, necessitating a dose reduction [1.4.5].
Anti-seizure Medications: Drugs like carbamazepine and phenytoin can decrease the effectiveness of DOACs like Eliquis, making blood clots more likely [1.4.3].

Herbal Supplements, Vitamins, and Foods

"Natural" does not mean safe. Many supplements and even some foods can cause significant interactions.

Supplements that Increase Bleeding Risk: Many popular supplements have their own blood-thinning properties, which can be dangerous when combined with medication. These include garlic, ginkgo biloba, ginger, fish oil, high-dose vitamin E, dong quai, and turmeric [1.2.2, 1.9.2, 1.3.5].
Supplements that Decrease Effectiveness: St. John's wort is a potent supplement that can significantly reduce the effectiveness of blood thinners like warfarin and Eliquis, increasing the risk of clots [1.2.2, 1.4.3, 1.5.5]. Green tea and Coenzyme Q10 may also increase clot risk with warfarin [1.9.5].
Food Interactions (Especially with Warfarin): While DOACs are less affected by diet, warfarin's effectiveness is highly dependent on a consistent intake of Vitamin K. This vitamin is crucial for blood clotting [1.9.4]. Foods rich in Vitamin K include leafy greens like spinach, kale, and broccoli [1.9.1, 1.9.5]. Patients on warfarin should not avoid these healthy foods but must maintain a consistent intake from day to day [1.9.3]. Grapefruit and cranberry juice can also interact, increasing the effect of some blood thinners [1.9.2, 1.9.3].

Comparison Table of Common Interactions


Interacting Agent Class	Examples	Blood Thinner(s) Affected	Primary Risk
NSAIDs	Ibuprofen, Naproxen, Aspirin	All (Warfarin, DOACs)	Increased bleeding, especially GI tract [1.2.5, 1.6.2]
Antibiotics	Ciprofloxacin, Clarithromycin, Metronidazole	Primarily Warfarin, some DOACs	Increased bleeding [1.7.1, 1.7.3]
Antifungals	Fluconazole, Ketoconazole	Warfarin and DOACs	Increased bleeding [1.4.3, 1.7.2]
Antidepressants (SSRIs/SNRIs)	Sertraline, Fluoxetine, Duloxetine	All (Warfarin, DOACs)	Increased bleeding [1.2.4, 1.8.2]
Herbal Supplements	St. John's Wort	Warfarin and DOACs	Decreased effectiveness (clot risk) [1.2.2, 1.5.5]
Herbal Supplements	Garlic, Ginkgo Biloba, Fish Oil	All	Increased bleeding [1.2.2, 1.5.1]
Vitamin K-rich Foods	Spinach, Kale, Broccoli	Warfarin	Decreased effectiveness (clot risk) if intake is inconsistent [1.9.4]

Conclusion: Prioritize Communication with Your Healthcare Provider

Managing a blood thinner regimen requires constant vigilance and open communication with your healthcare team. Before starting, stopping, or changing the dose of any medication—whether it's a prescription, an over-the-counter drug, or a dietary supplement—you must consult your doctor or pharmacist [1.2.2]. Simple actions like reading the 'Drug Facts' label on OTC products can help you identify potentially harmful ingredients like NSAIDs [1.2.5]. Always inform all your healthcare providers, including dentists, that you are taking a blood thinner. By being an informed and proactive patient, you can significantly reduce the risk of a dangerous drug interaction and ensure your medication works safely and effectively.

For more information from an authoritative source, you can visit the Mayo Clinic's page on Warfarin side effects and interactions. [1.3.5]

Frequently Asked Questions

Generally, yes. Acetaminophen is considered a safer pain relief alternative to NSAIDs for people on blood thinners. However, you should not exceed recommended doses and should consult your doctor, as very high doses can interact with warfarin [1.6.4, 1.3.2].

Acetaminophen (Tylenol) is the most commonly recommended over-the-counter pain reliever for those on anticoagulants. For more severe pain, you must speak with your doctor about prescription options that are safe to use with your specific blood thinner [1.6.4].

No, not without a doctor's approval. Many supplements, including turmeric, fish oil, garlic, and ginkgo biloba, have blood-thinning properties that can add to the effect of your medication and increase your risk of serious bleeding [1.9.2, 1.2.3].

Many common antibiotics can interfere with how your body processes blood thinners, particularly warfarin. This can cause the level of anticoagulant in your blood to rise to dangerous levels, significantly increasing your risk of bleeding. Always tell the prescribing doctor you are on a blood thinner [1.7.1, 1.7.3].

No, you don't have to avoid them, but you must be consistent. Foods high in Vitamin K, like spinach and kale, can make warfarin less effective. The key is to eat a consistent amount of these foods each week so your warfarin dose can be properly adjusted and remain stable [1.9.4, 1.9.5].

You should limit alcohol consumption. Heavy drinking can affect how your blood clots and how your body metabolizes the medication, increasing your risk of bleeding. Discuss safe limits with your healthcare provider [1.9.2, 1.9.4].

Yes, it is a significant problem. St. John's wort can make blood thinners like warfarin and DOACs (e.g., Eliquis) less effective by speeding up their breakdown in the body. This increases your risk of developing a dangerous blood clot and should be avoided [1.4.3, 1.5.5].