The enormous therapeutic and financial success of Viagra in the treatment of male impotence, plus basic similarities in the physiology of male and female sexual response, are leading some companies to explore similar pharmaceutical approaches to the more widespread problem of female sexual dysfunction. But will women's sexual problems be as amenable to drug therapy as men's? Should we be looking for a "little pink pill" any time soon? Part one of a series.

Last year, Pfizer's worldwide revenue from sales of the anti-impotence drug Viagra exceeded $1.3 billion, up roughly 30% from $1.0 billion in 1999. These are numbers to warm the heart of many a pharmaceutical shareholder, and the drug has only been on the market since April of 1998. It seems a substantial number of men had never sought medical help for their sexual dysfunction before Viagra, or they might have sought treatment but, for one reason or another, found the existing alternatives unacceptable. In other words, Pfizer successfully identified and brought valuable service to a large untapped market. And with this kind of success in their sights, others in the pharmaceutical industry set forth to find the next Viagra -- a "Zantac" to Pfizer's "Tagamet," as it were.

Sexual dysfunction more common among women

This particular contest, perhaps not surprisingly, centers on men. But consider the following statistics from the 1992 National Health and Social Life Survey (NHSLS): sexual problems are substantially more prevalent among women (43%) than men (31%). Those data further indicate that the specific problem of erectile dysfunction (ED) affects 5% of men overall, while the specific problem of female sexual arousal disorder (FSAD) affects 14% of women.

Beyond this apparently strong potential need for a therapy among women, developers also are well aware that the circulatory (vascular) processes of sexual arousal in women are similar to those of penile erection in men -- involving increased flow and accumulation of blood in the genital areas. Enhancing these vascular phenomena is precisely what Viagra is designed to do, and the notion that this or a similar product might work in women is now being put to the test.

A handful of small, preliminary studies (and a number of overenthusiastic press reports) hint that Viagra may be useful to treat some variants of female sexual dysfunction (FSD). Small wonder then, that several drug companies working on vascular solutions to erectile dysfunction in men are also targeting FSD, simultaneously, as they attempt to grab a piece of the Viagra pie. But before you call your broker to get in on the action, a word of caution.

Jury still out on 'Lady Viagra'

Three small studies in women whose FSD occurred as a side effect of antidepressant therapy suggest a therapeutic effect from Viagra. However, all three studies were uncontrolled, meaning there was no placebo (sugar pill) group against which to compare results. What's more, the largest of these studies included just 31 women, which is a very small enrollment by clinical standards.

Another uncontrolled trial, this one in 33 postmenopausal women with FSD, reported significant improvement in vaginal lubrication and clitoral sensitivity with Viagra, but only six women (18%) had significant improvement in actual sexual function. (For comparison, Viagra is reported to be effective in about 70% of men with erectile dysfunction.) In an interview, the principal investigator in this study later theorized that some of this perceived benefit may well have been a "placebo effect."

To date, the largest and, statistically speaking, most powerful placebo-controlled study of Viagra for FSD enrolled 583 estrogenized women with female sexual arousal disorder (FSAD). FSAD is the variation of female sexual dysfunction most similar to male erectile dysfunction: the physical signs of female sexual arousal such as increased vaginal lubrication, swelling and eversion (opening out) of the labia, and enlargement and elongation of the clitoris are, like the male erection, all affected by increased flow and pooling of blood. You'd think if Viagra were going to be effective in any particular group women with sexual problems, it would be women with arousal difficulties, but the investigators reported they were unable to detect any improvement in sexual response.

A number of other placebo-controlled studies of Viagra in FSD have been published or reported. In one, 17 postmenopausal or post-hysterectomized women took Viagra, were sexually stimulated with a 15-minute erotic video and a vibrator, and then were evaluated for signs of sexual response. The stimulation/evaluation procedure was repeated after the women took a placebo, and the results were compared. The one significant measurable change with Viagra was an increase in vaginal pH, but there were subjective reports from some women of increased sexual response to the stimulation. Two other placebo-controlled studies of Viagra found more substantial benefit: In one of them, 19 women with sexual dysfunction secondary to spinal cord injury found significant improvement in sexual response. And in a study of 51 young women with various arousal problems, Italian researchers reported major gains from Viagra, including indirect benefits to enjoyment and orgasm.

Researchers have yet to reach consensus on Viagra's potential as a therapy for sexual arousal problems in women, and 'Lady Viagra' appears to be a long shot. But the momentum for an alternative remains substantial, and several other biomedical companies are in the hunt.