Propecia (finasteride) has been approved for the treatment of male pattern baldness. Propecia is the first drug available in pill form.
In men with mild to moderate hair loss, clinical trials showed that 83% of the male patients had kept their hair or grown more after one year of treatment.
Side effects reported in approximately 2% of patients included a diminished desire for sex, difficulty achieving an erection, and/or a decreased amount of semen. The drug will not be marketed for women because safety and effectiveness have not bee established in women, and it is associated with birth defects.
The drug's active ingredient, finasteride, is already approved for the treatment of prostate enlargement. It works by blocking an enzyme called 5-alpha reductase, which is responsible for the formation of dihydro-testosterone in a man's body. The enzyme converts testosterone to DHT, and it is believed that DHT is a key factor in male pattern hair loss. Finasteride decreases the concentration of DHT in a man's scalp by about two-thirds.