Amoxicillin and Methacycline: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Jul 11, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Amoxicillin
Methacycline
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased antibacterial effectiveness
Interaction Deep Dive
Bacteriostatic drugs, such as the tetracyclines, may interfere with the bactericidal effect of penicillin3. Such concomitant use should be avoided 1.
Why it happens (mechanism)
Decreased bactericidal activity
Literature reports
1 report — tap to read
a) In a review of 43 adult patients seen in one medical facility during 1950 to 1960 with a diagnosis of pneumococcal meningitis, 7 received treatment with penicillin plus a tetracycline. Of these 7 patients, 6 died (mortality of 85%). While not the only contributing factor in the clinical outcome of these patients, the antibiotic antagonism is worth noting 2.
Common questions
Can I take Amoxicillin and Methacycline together?
Decreased antibacterial effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Amoxicillin and Methacycline interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Amoxicillin or Methacycline need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (3)
- Product Information: Vibramycin(R) Monohydrate oral suspension, doxycycline monohydrate oral suspension. Pfizer Labs (per FDA), New York, NY, 2013. DailyMed
- Olsson RA, Kirby JC, & Romansky MJ: Pneumococcal meningitis in the adult. Clinical, therapeutic, and prognostic aspects in forty-three patients. Ann Intern Med 1961; 55:545-549. PubMed
- Moellering RC Jr: Rationale for use of antimicrobial combinations. Am J Med 1983; 75(2A):4-8. DOI
Keep reading about Amoxicillin
Keep reading about Methacycline
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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