So, how does finasteride work? However, you must bear in mind that finasteride takes at least 3 months to start working. Finasteride The Quick Action Drug Used To Treat Benign Prostatic Hyperplasia In Men With An Enlarged Prostate By Vicki Jones The exact nature of your problems, and the expertise of the urologist you work with. How long does it take for finasteride to work for prostate . For hair loss, you can expect to see some improvement after 3 to 6 months. If finasteride will not work for you within 12 months of use, do not continue with the treatment because it will no longer benefit you. The prostate sits just below. New research also shows that the sexual and cognitive side effects of finasteride can persist for as long as ten years after men stopped taking the drug. How long does it take for finasteride to work? Studies have shown that finasteride decreases prostate specific antigen (psa) by approximately 50% during the first 12 months of use. In men, th...