Drug interactions
Cimetidine + Tamoxifen
Severity: Minor
Cimetidine 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
Cimetidine may alter tamoxifen metabolism through CYP inhibition, with an uncertain effect on active metabolite formation. The clinical impact on tamoxifen efficacy has not been clearly established.
What this interaction means in plain words
Cimetidine 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.
Cimetidine belongs to Gastrointestinal Tract; Tamoxifen belongs to Endocrine.
Why it happens
Cimetidine weakly inhibits CYP3A4 and other CYPs involved in tamoxifen metabolism; net effect on active metabolites is uncertain.
What to do
No routine adjustment is needed. Prefer famotidine if an acid suppressant is required in long-term tamoxifen therapy.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram 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 Cimetidine with Tamoxifen?
MediHelp rates the interaction as minor. Cimetidine 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. Cimetidine may alter tamoxifen metabolism through CYP inhibition, with an uncertain effect on active metabolite formation. The clinical impact on tamoxifen efficacy has not been clearly established.
How serious is the interaction between Cimetidine 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 routine adjustment is needed. Prefer famotidine if an acid suppressant is required in long-term tamoxifen therapy.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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