<prompt> Mechanism of action of finasteride is -Androgen receptor antagonist5 - a reductase inhibitor17 - a hydroxylase inhibitorAromatase inhibitor  <response>: Ans. is b i.e., 5-a reductase inhibitor Finasteride Competitive inhibitor of enzyme 5 a reductase, which converts testosterone to more active DHT Di hydro testosterone which is responsible for majority androgenic actions, including the actions on prostate and hair follicles. It is relatively selective for 5 a reductase type 2 isoenzyme which predominates in male urogenital tract, and is used in BPH, i.e., Benign prostatic hyperplasia to shrink the prostatic size and increase peak urinary flow rate. It has also been found effective in male pattern baldness.Adverse effects Decreased libido, impotence, decreased volume of ejaculate. Gynecomastia, skin rashes, lip swelling may occur. 