The long search for the female equivalent of Viagra has led researchers to . . . Viagra.
In a small study of 98 women published today, the little blue pill helped women whose sexual performance had flagged as a side effect of taking antidepressants, known as SSRIs -- a very specific finding that could open a new use for the male impotence drug.
The report in the Journal of the American Medical Assn. is one of the few to find some benefit for women despite nearly a decade of searching by its maker, Pfizer Inc.
More than 6 million women in the U.S. suffer from major depression. Antidepressants are the most common treatment for the mood disorder, and while they can be quite beneficial, they often have debilitating sexual side effects.
Doctors said the study, which was funded with a grant from Pfizer, could foster broader experimentation with Viagra for women, although they added that the drug was unlikely to become the blockbuster phenomenon it is among men. Its effectiveness in women is limited compared with men, and Pfizer has said it does not plan to develop the drug for female disorders.
Still, the study is certain to rekindle debate about the nature of sexual problems in women and men. While male difficulties have largely been seen in mechanical terms, female dysfunction has been viewed as more complicated and connected to desire.
But Dr. Irwin Goldstein, director of sexual medicine at Alvarado Hospital in San Diego, who has prescribed Viagra for some of his female patients, said the new research suggests that "however you think about men and women, there are a lot of similarities."
Not long after Viagra was introduced in 1998 to treat erectile dysfunction in men, Pfizer started researching its use in women. The company hoped to add to the success of Viagra, which had worldwide sales of $1.76 billion last year.
Initial studies of Viagra in women were disappointing. The drug blocks an enzyme that inhibits blood flow, which, in the case of men, allows more blood to flow to the penis. In women, the drug increased engorgement of genital tissue but failed to enhance women's enjoyment of sex. Pfizer ended company-initiated trials of the drug for female sexual arousal disorder in 2004.
However, many doctors said the early studies weren't selective enough, because they included women who lacked desire. Such women, like men with desire problems, couldn't expect to be helped by Viagra, they said.
The latest study was confined to women with arousal problems. They all had been diagnosed with major depression and were taking a specific class of antidepressants called selective serotonin re-uptake inhibitors, or SSRIs. Their depression was in remission when the study began.
The women, all of whom were premenopausal, were divided into two groups. One group was assigned to take Viagra one to two hours before sexual activity for eight weeks. The other women received the same instructions but were given a placebo.
At the end of the study, 72% of women taking Viagra, and 27% of those taking the placebo, reported improvement. The side effects were those typically associated with Viagra, including headaches and flushing. The women who responded best tended to have higher levels of testosterone, a phenomenon also observed in men taking Viagra.
Goldstein, who consults for Pfizer and other drug companies, said testosterone levels may be the key. A recent study in Italy found that Viagra helped female diabetics with normal testosterone levels.
"What is so cool about this paper is that women with sexual problems have another drug they can use," Goldstein said. "As long as their testosterone values are OK, we can help them."
Julia R. Heiman, director of the Kinsey Institute for Research in Sex, Gender and Reproduction at Indiana University and a study author, said the findings were important because the sexual side effects of antidepressants can be so debilitating that women discontinue the medication, putting themselves at risk for greater depression.
"This will change practice," said Dr. Andrew Leuchter, a professor of psychiatry at UCLA who was not involved in the study.
Dr. Glenn D. Braunstein, an endocrinologist and chairman of the department of medicine at Cedars-Sinai Medical Center, said Viagra might not work as well in the real world as it did in the study. Patients who experienced headaches or flushing might have figured out that they had received Viagra, and that knowledge might have affected their assessment of their sexual performance, he said.
"This is a provocative study, but I would love to see it confirmed in a larger group of women," he said.
Nonetheless, Braunstein predicted that few women on antidepressants would wait for a second study.
"If I had to predict, use of Viagra will go up," he said. "A woman might not even ask her gynecologist for it -- she might just ask her significant other to give her some."