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5-alpha reductase inhibitor (Type II) Pregnancy: Not for use in women. Pregnant women should not handle crushed tablets (masculinises male fetus).

Finasteride

Brand names: Proscar (BPH), Propecia (alopecia)

Adult dose

Dose: BPH: 5 mg once daily; Male pattern baldness: 1 mg once daily
Route: Oral
Frequency: Once daily
Max: 5 mg/day
BPH: 5 mg once daily for 6–12 months minimum (prostate shrinkage takes 3–6 months). Hair loss (Propecia): 1 mg once daily. Lowers PSA by ~50% after 6 months — adjust reference ranges accordingly.

Paediatric dose

Route: Oral
Frequency: Not applicable
Max: Not for use in children or women
Contraindicated in women and children. Women of childbearing potential must not handle crushed or broken tablets (5-alpha reductase inhibitors absorbed through skin — risk of feminisation of male fetus).

Dose adjustments

Renal

No dose adjustment required.

Hepatic

Use with caution in severe hepatic impairment.

Clinical pearls

  • PSA halved after 6 months — double measured PSA when interpreting results for prostate cancer screening
  • Reduces prostate volume and long-term risk of acute urinary retention
  • Combination with alpha-blocker (tamsulosin) more effective than monotherapy for symptomatic BPH (MTOPS trial)
  • Hair regrowth takes 3–6 months — discuss realistic expectations
  • Sexual side effects may persist after discontinuation (Post-Finasteride Syndrome)

Contraindications

  • Women (especially childbearing age — fetal risk via topical absorption)
  • Children
  • Hypersensitivity to finasteride

Side effects

  • Sexual dysfunction (reduced libido, erectile dysfunction, ejaculatory disorders)
  • Gynaecomastia
  • Post-finasteride syndrome (small number report persistent sexual/neurological side effects after stopping — controversial)
  • Reduced PSA (lowers PSA by ~50% — important for prostate cancer screening)
  • Rash

Interactions

  • No significant drug interactions identified

Monitoring

  • PSA (note 50% reduction baseline)
  • Urinary symptoms
  • Sexual function

Reference: BNFc; BNF; NICE NG118; EAU BPH Guidelines; MTOPS Trial. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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