Finasteride is in the class of medications called type II 5-alpha reductase inhibitors. By blocking 5-alpha reductase, finasteride blocks the conversion of testosterone to another male hormone, DHT. Decreasing the circulating DHT hormone can block its effect on hair follicles and the prostate gland. Unlike rogaine, which triggers hair regrowth, finasteride prevents hair loss by blocking the conversion of testosterone to DHT. DHT can bind to hair follicles in genetically predisposed people and miniaturize them.