Drug interactions
Metronidazole + Tamoxifen
Severity: Minor
Metronidazole and Tamoxifen: minor interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Tamoxifen is converted to N-desmethyltamoxifen by CYP3A4 and to endoxifen by CYP2D6. Metronidazole is a weak CYP3A4 inhibitor, and no meaningful loss of tamoxifen efficacy has been demonstrated.
What this interaction means in plain words
Metronidazole and Tamoxifen have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Metronidazole belongs to Anti Parasitic; Tamoxifen belongs to Endocrine.
Why it happens
Theoretical weak CYP3A4 inhibition by metronidazole altering tamoxifen metabolite formation.
What to do
No action is generally required for short antibiotic courses.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Metronidazole
- Ethanol + Metronidazole Contraindicated
- Metronidazole + Pimozide Contraindicated
- Amiodarone + Metronidazole Major
- Disulfiram + Metronidazole Major
- Ergotamine + Metronidazole Major
- Lomitapide + Metronidazole Major
Other interactions of Tamoxifen
- Amiodarone + Tamoxifen Major
- Anastrozole + Tamoxifen Major
- Bupropion + Tamoxifen Major
- Carbamazepine + Tamoxifen Major
- Cinacalcet + Tamoxifen Major
- Dacomitinib + Tamoxifen Major
Frequently asked questions
Can I take Metronidazole with Tamoxifen?
MediHelp rates the interaction as minor. Metronidazole and Tamoxifen have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Tamoxifen is converted to N-desmethyltamoxifen by CYP3A4 and to endoxifen by CYP2D6. Metronidazole is a weak CYP3A4 inhibitor, and no meaningful loss of tamoxifen efficacy has been demonstrated.
How serious is the interaction between Metronidazole and Tamoxifen?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No action is generally required for short antibiotic courses.
What other medicines interact with Metronidazole?
MediHelp also lists interactions of Metronidazole with, for example, Ethanol, Pimozide, Amiodarone. The full list is on the Metronidazole page.
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