The popular hair-growth drug finasteride, taken by millions of balding men, artificially lowers the results of the prostate-specific antigen (PSA) test, the standard screening test for prostate cancer, a multicenter study has found.
The study, involving 308 men ranging in age from 40 to 60 years old, is available online in the British medical journal The Lancet and is scheduled to be published after Jan. 1, 2007. The study calls for new clinical guidelines for primary-care physicians, dermatologists and urologists to account for the role of finasteride, known as Propecia when used for hair loss, while evaluating PSA results.
"It's not universally known that finasteride lowers PSA levels in younger men who take it for hair growth," said Dr. Claus Roehrborn, chairman of urology at UT Southwestern Medical Center and co-principal investigator of The Lancet study, along with Dr. Anthony D'Amico of Brigham and Women's Hospital and Dana-Farber Cancer Institute in Boston. "It is important for physicians to know that many young men take Propecia and that their PSA level is lowered artificially. Doctors need to adjust the PSA interpretation by multiplying it times two for these men."
Finasteride was initially developed in the 1990s for the treatment of benign prostatic hyperplasia (BPH), better known as enlarged-prostate disease, and was first approved by the U.S. Food and Drug Administration for this use. Patients with BPH must strain to pass urine and feel the urge to urinate frequently. BPH can lead to the inability to urinate and urinary tract infection.
In 1997 the FDA approved finasteride for the treatment of male-pattern baldness. While Propecia is administered at 1 milligram per day, patients who take the finasteride drug Proscar for BPH get a five times higher dosage, 5 mg per day.
"The impact of finasteride on PSA levels is significant," said Dr. Roehrborn. "This needs to be realized by all internists, family-care doctors, dermatologists - anybody who writes prescriptions for male-pattern hair loss."
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."