Drug interactions
Diphenhydramine + Tamoxifen
Severity: Moderate
Diphenhydramine 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
Diphenhydramine is a CYP2D6 inhibitor and may lower endoxifen formation from tamoxifen. With occasional use the effect is likely small, but regular long-term use could reduce tamoxifen effectiveness.
What this interaction means in plain words
Diphenhydramine 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.
Diphenhydramine belongs to Respiratory; Tamoxifen belongs to Endocrine.
Why it happens
Inhibition of CYP2D6 reduces conversion of tamoxifen to endoxifen.
What to do
Prefer a non-CYP2D6-inhibiting antihistamine such as loratadine or fexofenadine for regular use in tamoxifen patients.
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
Other interactions of Diphenhydramine
Frequently asked questions
Can I take Diphenhydramine with Tamoxifen?
MediHelp rates the interaction as moderate. Diphenhydramine 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. Diphenhydramine is a CYP2D6 inhibitor and may lower endoxifen formation from tamoxifen. With occasional use the effect is likely small, but regular long-term use could reduce tamoxifen effectiveness.
How serious is the interaction between Diphenhydramine 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: Prefer a non-CYP2D6-inhibiting antihistamine such as loratadine or fexofenadine for regular use in tamoxifen patients.
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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