Finasteride (5 alpha-reductase inhibitor) 💊

Always check the BNF here for up-to-date prescribing advice.

• Check BNF or equivalent for current prescribing information.
• Used in benign prostatic hypertrophy (BPH) and male pattern hair loss.

⚙️ Mode of Action

• Finasteride is a 5-alpha-reductase inhibitor.
• Blocks conversion of testosterone to dihydrotestosterone (DHT).
• Reduces prostate size ➝ improves urinary flow and symptoms of obstruction.
• Takes several months for full clinical effect.

📋 Indications / Dose

• Benign prostatic hypertrophy (BPH): 5 mg OD PO.
• Male pattern baldness: 1 mg OD PO.

🔄 Interactions

• See BNF for full interaction list.
• Generally few significant interactions, but monitoring advised if co-prescribed with other prostate/androgen-related therapies.

⚠️ Cautions

• Exclude prostate cancer before starting treatment (check PSA).
• Use with caution in patients with urinary tract obstruction.
• Monitor symptoms and PSA during treatment.

⛔ Contraindications

• Women and children (not indicated).
• Potential teratogen to male fetuses ➝ avoid handling crushed tablets during pregnancy (drug can be secreted in semen).

⚡ Side Effects

• Sexual: reduced libido, erectile dysfunction, decreased ejaculate volume.
• Breast: gynaecomastia, breast tenderness.
• Psychiatric: depression (rare but reported).
• PSA levels decrease by ~50% ➝ must interpret results cautiously when screening for prostate cancer.

📚 References

• BNF – Finasteride
• MHRA Drug Safety Update – Finasteride and psychiatric/sexual side effects.