Dutasteride: 5-Alpha Reductase Inhibitor for BPH and Androgenetic Alopecia
Dutasteride (Avodart) is a dual inhibitor of both type 1 and type 2 5-alpha reductase enzymes, blocking the conversion of testosterone to dihydrotestosterone (DHT) — more completely than finasteride (which inhibits type 2 only).
Approved for benign prostatic hyperplasia (BPH) in men with moderately enlarged prostate. Off-label for androgenetic alopecia (especially in men not responding to finasteride). Reduces DHT levels by ~95% (vs. ~70% with finasteride).
Mechanism of Action
Inhibits both type 1 (skin, liver) and type 2 (prostate, scalp) 5-alpha reductase isoforms, reducing DHT production by ~95%. DHT is the primary androgen responsible for prostate enlargement and androgenetic hair follicle miniaturisation.
Indications & Use
BPH: reduces prostate volume, improves urinary symptoms, reduces risk of acute urinary retention and need for surgery. Often combined with alpha-blockers (CombAT study). Off-label: androgenetic alopecia in men, women with hyperandrogenism (with caution).
Dosage
BPH: 0.5 mg once daily (take at the same time each day; capsules must not be crushed or opened). Hair loss: 0.5 mg/day off-label. Up to 6 months needed to see full benefit.
Side Effects
Sexual: decreased libido, erectile dysfunction, ejaculatory disorders (7–12%) — may persist after stopping (rare post-finasteride/dutasteride syndrome). Gynaecomastia. Very rare: depression, suicidal ideation. Increases risk of high-grade prostate cancer (slightly).
Drug Interactions
CYP3A4 inhibitors (ketoconazole, ritonavir): increase dutasteride levels. Alpha-blockers (tamsulosin): additive benefit in BPH — CombAT combination approved. No significant interactions with most common medications.
Contraindications
Women and children (teratogenic — causes feminisation of male foetus; women of childbearing potential must not handle crushed capsules). Hypersensitivity to 5-ARI.
Frequently Asked Questions
How does dutasteride compare to finasteride for hair loss?
Dutasteride inhibits both type 1 and type 2 5-alpha reductase (vs. finasteride type 2 only), reducing DHT by ~95% vs. ~70%. In head-to-head studies, dutasteride 0.5 mg was more effective than finasteride 1 mg for androgenetic alopecia. It is off-label but widely used by dermatologists.
Can dutasteride permanently affect sexual function?
The 'post-finasteride syndrome' describes persistent sexual side effects after stopping 5-ARIs — including persistent low libido, erectile dysfunction, and cognitive changes. While controversial and rare, it has been reported. Patients should be counselled about this rare possibility before starting.
Why can women not handle dutasteride capsules?
Dutasteride is teratogenic — it can feminise a male foetus (ambiguous genitalia). Pregnant women or women of childbearing potential must not handle broken or crushed capsules (skin absorption risk). Intact capsules are coated and safe to handle if not broken.
References
- EMA Avodart SPC 2023
- Roehrborn CG et al. Urology 2002 (BPH)
- Olsen EA et al. JAAD 2006 (hair loss)
Medical Disclaimer: This information is for educational purposes only and does not replace professional medical advice.