Researchers have known for years that the same testosterone metabolism responsible for prostate growth also causes male-pattern baldness (called androgenic alopecia), Dr. Roehrborn said. Both BPH and male-pattern hair loss have to do with the male hormone testosterone, which is being converted to dihydrotestosterone (DHT) by an enzyme named 5-alpha reductase. DHT activates the genes responsible for the development of male-pattern hair loss. Finasteride interferes with this process by blocking 5-alpha reductase and preventing the conversion of testosterone to DHT.
The data in The Lancet study were collected by Dr. Roehrborn from 1998 to 2000 in cooperation with medical centers in Arizona, Colorado, Connecticut, Georgia, Indiana, Louisiana, Minnesota, New York, North Carolina, Oregon, Texas and Virginia.
The data in The Lancet study are derived from a study Dr. Roehrborn conducted with Merck & Co., Inc. in 2000. Dr. Roehrborn, discussing the reasons to publish this report now, said: "The data are published now out of recognition that there was an acknowledged gap in the primary-care community about the impact of Propecia on PSA levels. When doctors ask for their patients' medical history, they need to ask if they have taken any drugs for hair loss, and the doctors need to multiply the PSA readings by two."