About Finasteride 5 Alpha-Reductase Inhibitor, Synthetic anti-androgen. Mechanism of Action of Finasteride This synthetic 4-azasteroid derivative competitively inhibits steroid 5alpha reductase, which is an enzyme responsible for active androgen dehydrotestosterone (this enzyme influences the development of prostate gland, so decreasing level of this hormone relieve the symptoms associated with benign prostatic hyperplasia)from testosterone. Indications for Finasteride 1. Benign prostatic hyperplasia 2. 1st stage of prostate cancer 3. Hirsuitism 4. Acne 5. Adjuvant therapy of radical prostectomy 6. Androgenic baldness