Finasteride, a novel 4-azasteroid, is a breakthrough in the treatment and control of benign prostatic hyperplasia. Mechanistically, it inhibits the prostatic-specific enzyme 5-alpha reductase, thereby decreasing the conversion of testosterone to dihydrotestosterone. It is reportedly effective in reducing urinary symptoms and prostatic volume and increasing maximal urinary flow rate. Finasteride is also being investigated as a treatment for prostatic cancer.