DHT Blockade for Prostate and Hair Loss
Blocking DHT with 5-alpha-reductase inhibitors (finasteride or dutasteride) effectively treats both benign prostatic hyperplasia (BPH) and androgenetic alopecia, though the mechanisms and efficacy differ between these conditions. 1, 2
Mechanism of Action
DHT blockade works by inhibiting 5-alpha-reductase enzymes that convert testosterone to dihydrotestosterone:
- Finasteride selectively inhibits type II 5-alpha-reductase, reducing serum DHT by approximately 70% and prostatic tissue DHT by 80% 1, 2
- Dutasteride inhibits both type I and type II isoenzymes, achieving more complete DHT suppression—95% in serum and 94% in prostatic tissue 1, 3
The FDA label confirms finasteride competitively and specifically inhibits type II 5-alpha-reductase, forming a stable enzyme complex with extremely slow turnover (half-life ~30 days) 2
Efficacy for Prostate Issues (BPH)
For lower urinary tract symptoms attributed to BPH, 5-alpha-reductase inhibitors provide meaningful benefit, particularly in men with enlarged prostates (>30cc) or PSA >1.5 ng/mL: 1
- Prostate volume reduction of 15-25% at six months, with 20% reduction being typical 1, 4
- IPSS (symptom score) improvement of 3-4 points maintained for 6-10 years 1
- Efficacy requires patience—onset of action is slower than alpha-blockers, with gradual symptom improvement over months 1, 3
- Treatment reduces PSA levels by approximately 50% after one year; measured PSA should be doubled when screening for prostate cancer 1, 5
Critical caveat: The larger the prostate gland, the more pronounced the effects. Men with prostates <30cc or PSA <1.5 ng/mL show unreliable responses 1
Efficacy for Androgenetic Alopecia
For male pattern baldness, finasteride demonstrates substantial efficacy, particularly in younger men: 4
- 85% of patients aged 20-40 years stopped losing hair with finasteride treatment 4
- Significant decreases in anagen hair diameters of approximately 14% 6
- Treatment must be continuous—hair loss resumes when therapy is discontinued 4
The American College of Obstetricians and Gynecologists recognizes finasteride as an antiandrogen option for hirsutism, though it notes the optimal antiandrogen agent remains undefined 6
Important Clinical Considerations
Sexual side effects occur in approximately 2-4% more patients compared to placebo, including erectile dysfunction, decreased libido, and ejaculation disorders 5. The FDA label confirms these effects but notes testosterone levels actually increase by 10-20% while remaining within physiologic range 2
Monitoring requirements:
- PSA levels require interpretation adjustment—double the measured value after one year of therapy 1, 5
- No effect on cortisol, prolactin, thyroid function, or lipid profiles 2
- The hypothalamic-pituitary-testicular axis remains unaffected 2
Important pitfall: No clinical data support "triple androgen blockade" (adding finasteride or dutasteride to combined androgen blockade for prostate cancer)—this approach lacks evidence 1
The Paradox: DHT and Prostate Cancer
Interestingly, while DHT drives BPH, some research suggests elevated DHT levels in androgenic alopecia may actually protect against prostate cancer through increased prostaglandin D2 production 7. However, this remains theoretical and should not influence treatment decisions for symptomatic BPH or bothersome hair loss.
Bottom line: DHT blockade works for both conditions but requires realistic expectations—prostate symptom improvement takes months, hair loss prevention requires lifelong therapy, and neither condition is "solved" but rather managed effectively with continued treatment.