<p>Finasteride, a competitive inhibitor of the 5&alpha; reductase enzyme which is used in the treatment of benign prostatic hyperplasia. It is selective for 5&alpha; reductase type 2 enzyme and has no affinity for androgen receptors. The development of the prostate gland and subsequent BPH is dependent upon conversion of testosterone to dihydrotestosterone (DHT) within the prostate. Finasteride belongs to a new class of specific inhibitors of 5&alpha; reductase, an intracellular enzyme, which metabolises testosterone into the more potent androgen, DHT. Finasteride has no affinity for the androgen receptor.</p>