DHT or dihydrotestosterone is a derivative of the male sex hormone testosterone. The testosterone is naturally converted into DHT because of the action of an enzyme called type II 5-alpha reductase. While some amount of DHT is present in all men, in some men the DHT levels reach higher than normal. In men who have high levels of DHT, some DHT travels to the scalp where it attaches to the hair follicles. This DHT has a damaging effect on the hair follicles; it shrinks the follicle, causing the hair to fall out. Eventually the follicle becomes dormant and the growth of new hair is inhibited. If the DHT levels are not checked, the condition worsens causing men to suffer from partial or even complete baldness.

Thanks to the advancements in medical science, we now have medicines through which we can block the excess conversion of testosterone to DHT. Propecia finasteride is an FDA approved medication for male pattern hair loss that can effectively reverse male pattern baldness by blocking the conversion of testosterone to DHT. Propecia manages to do this as it belongs to a class of medicines called type II 5-alpha reductase inhibitors. Propecia inhibits the action of enzyme type II 5-alpha reductase and thereby puts a check on the conversion of testosterone to DHT. This helps to lower the DHT levels and thereby controls hair fall.