Finasteride is a 5α-reductase inhibitor. The enzyme 5α-reductase converts testosterone into dihydrotestosterone (DHT). The latter is required for proliferation of the prostate gland. Finasteride competes with testosterone for the enzyme.
Since the enzyme prefers finasteride, the concentration of DHT will decrease. The effect of prostate gland volume reduction is evident several months after onset of treatment.
Finasteride may NOT be prescribed in case of
Extra info: Due to the abnormal cell growth in the presence of a prostate tumor, the introduction of an enzyme that will increase testosterone levels is contraindicated.