How do 5-alpha-reductase inhibitors help in BPH and when is the expected improvement?

• A. Immediate urinary flow improvement within days
• B. No effect on size, only symptom relief
• C. Increase testosterone levels to reduce prostatic obstruction
• D. Prostate shrinkage by reducing dihydrotestosterone; improvement after 6–12 months.

Answer: (D)

5-alpha-reductase inhibitors work by blocking the conversion of testosterone to dihydrotestosterone in the prostate. DHT drives prostatic growth, so lowering DHT reduces androgenic stimulation and leads to a gradual shrinkage of the enlarged gland. Because this is a remodeling process, the improvement in urinary symptoms and obstruction doesn’t happen right away; it typically becomes noticeable after several months, most commonly around 6 to 12 months. PSA levels also fall as the prostate size decreases, reflecting the reduced tissue volume. Therefore, the correct description is that the drug shrinks the prostate by reducing DHT, with improvement expected after about 6–12 months.