Finasteride (Proscar, Propecia) and dutasteride (Avodart), inhibitors of the 5-a-reductase enzyme that prevent the conversion of testosterone into dihydrotestosterone (DHT). Finasteride blocks only 5-a-reductase type I, dutasteride also blocks type II. They are not general antiandrogens in that they don't counteract the effects or production of other androgens than DHT.

Proscar is used to treat a medical condition in men called benign prostatic hyperplasia or BPH. BPH is a condition where your prostate gland (which is near your bladder) has become bigger making it more difficult for you to pass urine. This can lead to symptoms such as:

• weak or interrupted stream of urine
• feeling that you cannot empty your bladder completely
• delay before you start to pass urine
• needing to pass urine often, especially at night
• feeling that you must pass urine right away

BPH occurs only in men and is common over the age of 50 years. BPH can lead to serious problems, including urinary tract infections and the sudden inability to pass urine at all.

The prostate gland takes years to grow. Therefore, the symptoms of BPH take a long time to develop. Proscar works by slowly reducing the size of your prostate gland. This may lead to gradual improvement in your urine flow and other symptoms over several months. Proscar also helps reduce the risk of developing a sudden inability to pass urine (acute urinary retention) and the need for surgery. This may happen whether or not you notice any improvement or change in symptoms.