Drug interactions
Finasteride + Phenytoin
Severity: Minor
Finasteride and Phenytoin: 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
Phenytoin is an inducer of CYP3A4 and may reduce finasteride concentrations. Given finasteride's wide margin, the clinical effect is probably small, but efficacy could be reduced with long-term use.
What this interaction means in plain words
Finasteride and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Finasteride belongs to Genitourinary; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing finasteride clearance.
What to do
No routine adjustment is needed. Evaluate clinical response to finasteride if symptoms persist or return.
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 Finasteride
- Finasteride + Levoketoconazole Moderate
- Finasteride + Nefazodone Moderate
- Finasteride + Rifampin Moderate
- Finasteride + St john's wort Moderate
- Amobarbital + Finasteride Minor
- Aprepitant + Finasteride Minor
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Finasteride with Phenytoin?
MediHelp rates the interaction as minor. Finasteride and Phenytoin have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Phenytoin is an inducer of CYP3A4 and may reduce finasteride concentrations. Given finasteride's wide margin, the clinical effect is probably small, but efficacy could be reduced with long-term use.
How serious is the interaction between Finasteride and Phenytoin?
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. Evaluate clinical response to finasteride if symptoms persist or return.
What other medicines interact with Finasteride?
MediHelp also lists interactions of Finasteride with, for example, Levoketoconazole, Nefazodone, Rifampin. The full list is on the Finasteride page.
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