Finasteride

Testosterone 5α-reductase type 2 inhibitors

ATC code: G04CB01

Brand names: Proscar, Propecia, Finasteride

Updated 24 Sep 2026 · Methodology

Indications

Androgenetic alopecia

First line

Finasteride 1 mg/day is first-line therapy for male androgenetic alopecia. Kaufman 1998 RCT (n=1879, 2 years) showed 86 hairs/cm² increase in vertex hair count, with sustained results during continued use. Effect plateaus by 12 months and persists only with continuous use – discontinuation leads to renewed hair loss. The drug is not approved in premenopausal women. Post-finasteride syndrome (PFS) – persistent sexual, cognitive, and emotional symptoms after discontinuation – has been reported in a small subgroup; incidence and causality remain debated. and BAD guidelines list finasteride as first-line for male androgenetic alopecia.

Used in men aged 18-41. Not approved in women (exception: postmenopausal patients off-label).

Sources

ICD-10: L64 · ICD-11: ED70.0

Benign prostatic hyperplasia

First line

Finasteride 5 mg/day is evidence-based first-line therapy for benign prostatic hyperplasia with prostate volume above 30–40 mL. The PLESS trial (Roehrborn 2002, n=3040, 4 years) showed 57% reduction in acute urinary retention risk and 55% reduction in surgery need versus placebo. Prostate volume shrinks by 20–25%, PSA by about 50% (important for prostate cancer screening interpretation). Effect develops over 6–12 months. Combination with α-blockers (tamsulosin, doxazosin) provides additional benefit on symptoms and progression risk (MTOPS, CombAT). AUA, EAU, and guidelines list finasteride as first-line for obstructive BPH with enlarged prostate.

Sources

ICD-10: N40 · ICD-11: GA90

Marketing claims without evidence base

The drug is promoted for these uses outside international guidelines. Each entry below is analyzed against AEMPS, FDA, EMA, Cochrane and major RCTs.

Anti-aging and longevity

Not recommended

Finasteride is a type II 5α-reductase inhibitor. It is prescribed for men with benign prostatic hyperplasia and androgenic alopecia; it is not indicated in women (AEMPS Ficha Técnica). Finasteride is prescribed to women of reproductive age for hair loss off-label and in anti-aging protocols. In women, clinical evidence for hair loss is insufficient, and the drug is teratogenic ( category X, risk of male fetal external genitalia development disruption – contact even through skin is contraindicated with broken tablets). In men, finasteride can cause reduced libido, erectile dysfunction, depression, and gynecomastia; a post-finasteride syndrome with prolonged adverse effects after discontinuation has been described. If finasteride was prescribed to a woman of reproductive age or to a man without confirmed indications, consider seeking a second opinion.

Sources

How to read tiers A–F

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit

Mechanism of action

Finasteride is a selective inhibitor of type 2 5α-reductase isoenzyme, which converts testosterone to dihydrotestosterone (DHT) in the prostate and hair follicles. At 1 mg/day, serum DHT drops by 65–70%; at 5 mg/day, by 70–75%. The effect on the prostate takes 6–12 months, on hair follicles 3–6 months. After discontinuation, DHT returns to baseline within 14–28 days.

Safety

Contraindications

Pregnancy (category X)
Age under 18
Hypersensitivity
Women of childbearing age (without contraception)

Serious adverse effects

Post-finasteride syndrome (PFS) – persistent sexual, cognitive, and emotional symptoms after discontinuation
Depression and suicidal ideation (rare reports)
Male breast cancer (rare)

Common adverse effects

Decreased libido (3–5%)
Erectile dysfunction (3–5%)
Decreased ejaculate volume
Gynaecomastia
Rash, pruritus

Pregnancy: can you take Finasteride?

AEMPS summary of product characteristics (section 4.6): finasteride is contraindicated in women because of the risk in pregnancy. If given to a pregnant woman, it may cause abnormalities of the external genitalia in a male fetus, because type II 5α-reductase inhibitors block the conversion of testosterone to dihydrotestosterone in some tissues.

Breastfeeding: can you take Finasteride?

The drug is not intended for women; if treatment is required, breastfeeding should be discontinued.

Calculate RID

Reference information, not a clinical decision. Discuss feeding pauses or changes with your physician or an IBCLC.

Practical notes

Russian practice note

In Russia, finasteride is registered as 5 mg (Proscar, generics) for BPH and 1 mg (Propecia) for alopecia. Generic 5 mg formulations cost 400–800 ₽/month. The 1 mg dose for alopecia is often obtained by splitting 5 mg tablets (off-label practice, not regulator-prohibited but not recommended by the manufacturer due to uneven active ingredient distribution). Finasteride lowers PSA by approximately half – measured PSA must be doubled when interpreting prostate cancer screening. Pregnancy category X: handling crushed tablets is contraindicated for pregnant women (risk of hypospadias in the male fetus).

Drug interactions

Clinically significant drug interactions are uncommon. Metabolised via CYP3A4, but at therapeutic doses does not affect concentrations of warfarin, digoxin, theophylline, or antipyrine. Combination with α-blockers (CombAT) enhances overall effect on BPH symptoms.

Label mentions19 mentions

Verbatim lines from the interaction sections, in the language of the label

From this drug’s label

MajorMinoxidil
«Debido a la ausencia de datos para el uso concomitante de finasterida y minoxidil tópico en la pérdida masculina del cabello, no se recomienda su uso concomitante.»
AEMPS, section 4.5 · Open on CIMA
Acetylsalicylic acid
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
benzodiazepinesclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
calcium channel blockersclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
Digoxin
«No se han identificado interacciones de fármacos con importancia clínica. Finasterida presenta un metabolismo de primer paso, pero no afecta al sistema enzimático del metabolismo de fármacos ligados…»
AEMPS, section 4.5 · Open on CIMA
Digoxin
«Cytochrome P450-Linked Drug Metabolizing Enzyme System: No drug interactions of clinical importance have been identified. Finasteride does not appear to affect the cytochrome P450-linked drug…»
FDA, section 7 · Open on DailyMed
diureticsclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
fluoroquinolonesclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
Glibenclamide
«No se han identificado interacciones de fármacos con importancia clínica. Finasterida presenta un metabolismo de primer paso, pero no afecta al sistema enzimático del metabolismo de fármacos ligados…»
AEMPS, section 4.5 · Open on CIMA
nitratesclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
NSAIDsclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
Propranolol
«No se han identificado interacciones de fármacos con importancia clínica. Finasterida presenta un metabolismo de primer paso, pero no afecta al sistema enzimático del metabolismo de fármacos ligados…»
AEMPS, section 4.5 · Open on CIMA
Propranolol
«Cytochrome P450-Linked Drug Metabolizing Enzyme System: No drug interactions of clinical importance have been identified. Finasteride does not appear to affect the cytochrome P450-linked drug…»
FDA, section 7 · Open on DailyMed
statinsclass named in the label
«Other Concomitant Therapy: Although specific interaction studies were not performed, finasteride was concomitantly used in clinical studies with acetaminophen, acetylsalicylic acid, α-blockers…»
FDA, section 7 · Open on DailyMed
Theophylline
«No se han identificado interacciones de fármacos con importancia clínica. Finasterida presenta un metabolismo de primer paso, pero no afecta al sistema enzimático del metabolismo de fármacos ligados…»
AEMPS, section 4.5 · Open on CIMA
Theophylline
«Cytochrome P450-Linked Drug Metabolizing Enzyme System: No drug interactions of clinical importance have been identified. Finasteride does not appear to affect the cytochrome P450-linked drug…»
FDA, section 7 · Open on DailyMed
Warfarin
«No se han identificado interacciones de fármacos con importancia clínica. Finasterida presenta un metabolismo de primer paso, pero no afecta al sistema enzimático del metabolismo de fármacos ligados…»
AEMPS, section 4.5 · Open on CIMA
Warfarin
«Cytochrome P450-Linked Drug Metabolizing Enzyme System: No drug interactions of clinical importance have been identified. Finasteride does not appear to affect the cytochrome P450-linked drug…»
FDA, section 7 · Open on DailyMed

From other drugs’ labels

Theophylline
«Drug Interactions:: finasteride Sorbitol (purgative doses do not inhibit»
FDA, section 7 · Open on DailyMed

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Frequently asked

What is Finasteride used for?

Finasteride is evaluated for the following indications with varying evidence strength: Androgenetic alopecia (evidence tier A), Benign prostatic hyperplasia (evidence tier A), Anti-aging and longevity (evidence tier F). See the full indication matrix with dosing and citations above on this page.

What are the side effects of Finasteride?

Common side effects of Finasteride (≥ 1 in 100): Decreased libido (3–5%), Erectile dysfunction (3–5%), Decreased ejaculate volume, Gynaecomastia, Rash, pruritus. See the Safety section for uncommon and serious reactions.

Is Finasteride safe during pregnancy?

Is Finasteride compatible with breastfeeding?

The drug is not intended for women; if treatment is required, breastfeeding should be discontinued.

Who should not take Finasteride?

Finasteride is contraindicated in: Pregnancy (category X); Age under 18; Hypersensitivity; Women of childbearing age (without contraception). Full list in the Safety section.

Official sources

Direct links to regulator labels. Open in a new tab.

AEMPS / CIMALabel dated 03/18/2026
FDA / DailyMedLabel dated 08/05/2026

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