What is the mechanism of action of Proscar (finasteride) for treating BPH?

Proscar (finasteride) works by inhibiting 5-alpha reductase, an enzyme that plays a critical role in the conversion of testosterone to dihydrotestosterone (DHT). DHT is the hormone primarily responsible for prostate growth and enlargement, particularly in benign prostatic hyperplasia (BPH).

By inhibiting the 5-alpha reductase enzyme, finasteride effectively reduces DHT levels in the body, which leads to a decrease in prostate size and alleviates symptoms associated with BPH, such as difficulty urinating. This mechanism is beneficial for treating conditions related to excess DHT, making finasteride a targeted therapeutic option for managing BPH.

The other options do not accurately reflect the drug's mechanism: finasteride does not inhibit testosterone synthesis, promote DHT production, or stimulate prostate enlargement. Instead, its role in blocking the conversion process directly addresses the underlying factor that contributes to prostate enlargement in BPH.