This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
Finasteride acts by blocking 
Select and explain. 
A. Alpha receptor, B. 5 alpha reductase enzyme, C. 5 alpha reductase enzyme, D. Beta receptors
B: 5 alpha reductase enzyme
Answer: B: 5 alpha reductase enzyme 
Explanation: Finasteride is a competitive inhibitor of the enzyme 5alpha-reductase which conves testosterone into more active DHT responsible for androgen action in many tissues. finasteride, dutasteride- used for prostate cancer and BPH (Ref.Essentials of medical pharmacology TD Tripathi 7th edition page no.302)