What Medications Cannot Be Taken With Amoxicillin?

October 10, 2025 •

2 min read

While approximately 10% of the U.S. population reports a penicillin allergy, many adverse drug reactions are due to interactions, not allergies. Understanding what medications cannot be taken with amoxicillin is crucial for safety and efficacy.

Quick Summary

Amoxicillin can interact with several common medications. These include certain blood thinners, gout medications like allopurinol and probenecid, methotrexate, and some other antibiotics, leading to increased risks of side effects or reduced effectiveness.

Key Points

Blood Thinners: Combining amoxicillin with anticoagulants like warfarin can increase your risk of serious bleeding.
Gout Medications: Taking allopurinol with amoxicillin increases the risk of skin rash, while probenecid can dangerously increase amoxicillin levels.
Methotrexate: Amoxicillin can raise methotrexate levels in the body, leading to a higher risk of toxicity.
Other Antibiotics: Bacteriostatic antibiotics (e.g., tetracycline) may reduce the bactericidal effectiveness of amoxicillin.
Live Vaccines: Amoxicillin can decrease the effectiveness of live oral vaccines, such as those for typhoid and cholera.
Oral Contraceptives: There is a potential, though debated, risk that amoxicillin may reduce the effectiveness of birth control pills.
Always Inform Your Doctor: To avoid interactions, always give your healthcare provider a full list of all medications, supplements, and vitamins you are taking.

Understanding Amoxicillin

Amoxicillin is a widely prescribed penicillin-type antibiotic used to treat a variety of bacterial infections. It works by killing bacteria through interfering with cell wall formation. Amoxicillin is effective against many types of bacteria and is well-absorbed by the body. However, potential drug interactions are a significant consideration when taking amoxicillin.

Major Drug Interactions with Amoxicillin

Always inform your healthcare provider about all medications and supplements you are taking before starting amoxicillin. Several drugs can interact with amoxicillin.

Blood Thinners (Anticoagulants)

Combining amoxicillin with blood thinners such as warfarin, apixaban, or rivaroxaban can increase the risk of bleeding. Amoxicillin may affect gut bacteria involved in Vitamin K production, which is important for clotting. This can enhance the effect of anticoagulants. Close monitoring of blood clotting levels (like INR) may be needed.

Gout Medications

Interactions exist with gout medications:

Allopurinol (Zyloprim): Concurrent use of allopurinol and amoxicillin increases the risk of skin rash.
Probenecid: Probenecid can increase the levels of amoxicillin in the blood by affecting kidney function, potentially leading to more side effects.

Methotrexate

Amoxicillin can decrease the body's ability to eliminate methotrexate. This can lead to higher levels of methotrexate and an increased risk of toxicity and side effects. Close monitoring is necessary if these drugs are taken together.

Other Antibiotics

Combining amoxicillin (a bactericidal antibiotic) with bacteriostatic antibiotics (like tetracyclines or macrolides) can interfere with amoxicillin's effectiveness.

Live Vaccines

Amoxicillin can reduce the effectiveness of live oral vaccines, specifically the typhoid and cholera vaccines. A waiting period is recommended between finishing amoxicillin and receiving these vaccines.

Oral Contraceptives (Birth Control Pills)

The potential for amoxicillin to reduce the effectiveness of oral contraceptives is debated. Current guidelines often state that only rifamycin antibiotics significantly impact birth control. However, some healthcare providers still recommend using a backup birth control method while taking antibiotics.

Comparison Table of Amoxicillin Interactions


Medication/Class	Interacting Drug Examples	Potential Effect	Management Recommendation
Blood Thinners	Warfarin, Apixaban, Rivaroxaban	Increased risk of bleeding	Frequent monitoring (INR); dose adjustment
Gout Medications	Allopurinol, Probenecid	Increased risk of skin rash (Allopurinol); increased amoxicillin side effects (Probenecid)	Avoid combination if possible; monitor for rash
Immunosuppressants	Methotrexate	Increased risk of methotrexate toxicity	Close monitoring; potential dose adjustment
Other Antibiotics	Tetracycline, Erythromycin	May interfere with amoxicillin's effectiveness	Avoid combining bacteriostatic and bactericidal drugs
Live Oral Vaccines	Typhoid Vaccine, Cholera Vaccine	Reduced vaccine effectiveness	Separate administration by several days/weeks
Oral Contraceptives	Ethinyl estradiol combinations	Potentially reduced contraceptive effectiveness (controversial)	Discuss with doctor; consider using backup contraception

Conclusion

Amoxicillin is an effective antibiotic, but being aware of its potential interactions with other medications is vital for patient safety and treatment success. Interactions with drugs like blood thinners, certain gout medications, methotrexate, and specific vaccines can lead to adverse outcomes or reduced efficacy. Always provide your healthcare provider with a complete list of all medications to prevent harmful interactions.

For more detailed information on penicillin allergies, you can visit the CDC page on Penicillin Allergy.

Frequently Asked Questions

Taking amoxicillin with blood thinners such as warfarin, apixaban, or rivaroxaban may increase your risk of bleeding. Your doctor will need to monitor you closely if this combination is necessary.

Yes. Taking amoxicillin with allopurinol increases the risk of developing a skin rash. Taking it with probenecid can raise the concentration of amoxicillin in your blood, increasing the risk of side effects.

Amoxicillin can interfere with your body's ability to clear methotrexate, leading to increased levels of the drug and a higher risk of serious side effects and toxicity.

While some sources suggest amoxicillin might reduce the effectiveness of oral contraceptives, most current evidence indicates this is not a significant risk for most antibiotics, except for the rifamycin class. However, to be safe, discuss using a backup method of contraception with your doctor.

It depends on the types. Combining amoxicillin (a bactericidal antibiotic) with a bacteriostatic antibiotic (like tetracycline or erythromycin) is generally advised against as it may reduce amoxicillin's ability to kill bacteria.

Amoxicillin can reduce the effectiveness of live oral vaccines, specifically the typhoid and cholera vaccines. You should wait at least 3 days after finishing amoxicillin before getting a live typhoid vaccine.

While not strictly prohibited, healthcare professionals often recommend avoiding alcohol. It can increase common side effects of amoxicillin like nausea and abdominal discomfort.