Drug interactions
Rifampin + Tamoxifen
Severity: Major
Rifampin and Tamoxifen: major 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
Rifampin is a potent enzyme inducer and markedly lowers tamoxifen and endoxifen concentrations. This may reduce the anti-cancer effect of tamoxifen.
What this interaction means in plain words
Rifampin and Tamoxifen can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Rifampin induces CYP3A4 and CYP2C9, increasing metabolic clearance of tamoxifen and its metabolites.
What to do
Avoid the combination when an alternative antimycobacterial regimen is possible. If rifampin is essential, consider an alternative endocrine therapy and monitor for reduced response.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Rifampin and Tamoxifen, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 14 days on the web. No card needed.
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 Rifampin with Tamoxifen?
MediHelp rates the interaction as major. Rifampin and Tamoxifen can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Rifampin is a potent enzyme inducer and markedly lowers tamoxifen and endoxifen concentrations. This may reduce the anti-cancer effect of tamoxifen.
How serious is the interaction between Rifampin and Tamoxifen?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination when an alternative antimycobacterial regimen is possible. If rifampin is essential, consider an alternative endocrine therapy and monitor for reduced response.
What other medicines interact with Tamoxifen?
MediHelp also lists interactions of Tamoxifen with, for example, Amiodarone, Anastrozole, Bupropion. The full list is on the Tamoxifen page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
