Drug interactions
St john's wort + Tamoxifen
Severity: Moderate
St john's wort and Tamoxifen: moderate 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
St John's wort induces CYP3A4 and P-glycoprotein, which may lower tamoxifen and endoxifen concentrations. This could reduce the therapeutic benefit in breast cancer.
What this interaction means in plain words
St john's wort and Tamoxifen can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Induction of CYP3A4 by hyperforin increases tamoxifen metabolic clearance.
What to do
Advise patients to avoid St John's wort while taking tamoxifen. Use another option for mood symptoms or hot flushes.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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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
Frequently asked questions
Can I take St john's wort with Tamoxifen?
MediHelp rates the interaction as moderate. St john's wort and Tamoxifen can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. St John's wort induces CYP3A4 and P-glycoprotein, which may lower tamoxifen and endoxifen concentrations. This could reduce the therapeutic benefit in breast cancer.
How serious is the interaction between St john's wort and Tamoxifen?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Advise patients to avoid St John's wort while taking tamoxifen. Use another option for mood symptoms or hot flushes.
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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