How do 5-alpha-reductase inhibitors help treat BPH?

Marc B. Garnick, MD
Hematology & Oncology
In the treatment of benign prostatic hyperplasia (BPH), or prostate enlargement, 5-alpha-reductase inhibitors help shrink the prostate, but they work slowly and may be less effective at relieving symptoms than the alpha blockers. Finasteride and dutasteride shrink the prostate by changing its hormone balance. Specifically, they reduce levels of the male hormone dihydrotestosterone (DHT), which plays a role in prostate growth. The drugs interfere with the action of 5-alpha-reductase, an enzyme that converts testosterone to DHT. Interestingly, their ability to lower DHT levels also makes these drugs useful in treating hair loss in men.

An analysis of six studies comparing finasteride against a placebo found that the medication works somewhat better in men with large prostates, and that it may not be a good choice for those with smaller glands.

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