Merck, which has major operations in the Philadelphia area, on Tuesday said through spokesman Ron Rogers: "We are aware of the lawsuits, and we intend to vigorously defend against them."
Finasteride was first approved in the United States in 1992 as Proscar, a treatment for benign enlargement of the prostate gland. A lower dose, Propecia, was approved in 1997 for male pattern baldness, but balding men often buy the higher-dose product and split the tablet to save money.
The litigation comes as a growing number of physicians, studies, and patient websites are warning of a small but significant chance of irreversible sexual effects, including impotence, from finasteride.
"My message is that clinicians who are going to prescribe this drug for hair loss should sit down and have a candid, serious discussion about the risks and benefits, and warn their patients that in some men - not all - these sexual side effects are persistent," said Abdulmaged M. Traish, a Boston University professor of biochemistry and urology who in December published a review of finasteride studies. "For some men, it's a life sentence."
Finasteride works by blocking the conversion of testosterone into an even more potent male sex hormone that is crucial to sexual development and function. The same potent hormone can attack hair follicles, so blocking it can interrupt hair loss.
Merck's U.S. labeling and website warn that some men suffer problems such as decreased libido, erectile dysfunction, and decreased ejaculate. However, the company says these problems are unusual - occurring in fewer than 2 percent of men on Propecia - and get better.
"These side effects decreased to 0.3 percent of men or less by the fifth year" on Propecia, the website says. "These side effects went away in men who stopped taking Propecia because of them."
