Drug interactions
Letrozole + Tamoxifen
Severity: Major
Letrozole 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
Co-administration lowers letrozole concentrations and offers no efficacy advantage in breast cancer. The combination is therefore not recommended, whereas sequential use is accepted practice.
What this interaction means in plain words
Letrozole 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.
Letrozole belongs to Oncology; Tamoxifen belongs to Endocrine.
Why it happens
Tamoxifen reduces letrozole plasma levels, probably through induction of its metabolism, though the mechanism is not well established.
What to do
Do not use together; give letrozole sequentially after completing tamoxifen if indicated.
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?
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Other interactions of Tamoxifen
- Amiodarone + Tamoxifen Major
- Anastrozole + Tamoxifen Major
- Bupropion + Tamoxifen Major
- Carbamazepine + Tamoxifen Major
- Cinacalcet + Tamoxifen Major
- Dacomitinib + Tamoxifen Major
Other interactions of Letrozole
Frequently asked questions
Can I take Letrozole with Tamoxifen?
MediHelp rates the interaction as major. Letrozole 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. Co-administration lowers letrozole concentrations and offers no efficacy advantage in breast cancer. The combination is therefore not recommended, whereas sequential use is accepted practice.
How serious is the interaction between Letrozole 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: Do not use together; give letrozole sequentially after completing tamoxifen if indicated.
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.
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