Pharmacology
The enzyme 5α-reductase is involved in the conversion of testosterone to the active form dihydrotestosterone (DHT) by reducing the Δ4,5 double-bond. In benign prostatic hyperplasia, dihydrotestosterone acts as a potent cellular androgen and promotes prostate growth; therefore, inhibiting the enzyme reduces the excessive prostate growth. In alopecia, male-pattern baldness is one of the effects of androgenic receptor activation. Thus, reducing the levels of dihydrotestosterone reduces alopecia.
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