Drug interactions
Finasteride + Phenobarbital
Severity: Minor
Finasteride and Phenobarbital: 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
Phenobarbital is an established CYP3A4 inducer and may reduce finasteride concentrations over time. Loss of therapeutic effect is possible with chronic use but is not well documented.
What this interaction means in plain words
Finasteride and Phenobarbital have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Why it happens
Induction of CYP3A4 increasing finasteride clearance.
What to do
No empirical dose change; review finasteride efficacy (urinary symptoms, PSA or hair response) during long-term co-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 Finasteride
- Finasteride + Levoketoconazole Moderate
- Finasteride + Nefazodone Moderate
- Finasteride + Rifampin Moderate
- Finasteride + St john's wort Moderate
- Amobarbital + Finasteride Minor
- Aprepitant + Finasteride Minor
Frequently asked questions
Can I take Finasteride with Phenobarbital?
MediHelp rates the interaction as minor. Finasteride and Phenobarbital have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Phenobarbital is an established CYP3A4 inducer and may reduce finasteride concentrations over time. Loss of therapeutic effect is possible with chronic use but is not well documented.
How serious is the interaction between Finasteride and Phenobarbital?
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 empirical dose change; review finasteride efficacy (urinary symptoms, PSA or hair response) during long-term co-therapy.
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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