Nov. 19, 2009 -- An investigational drug that didn't perform well as an antidepressant appears to slightly boost sexual desire as well as the number of satisfying sexual encounters in women with lagging libidos, a study shows.
The research was presented this week at the 12th Congress of the European Society for Sexual Medicine in Lyon, France.
Some wonder if the drug, called flibanserin, will be the new ''female Viagra," but critics say the effect is minimal. Meanwhile, the manufacturer is planning additional clinical trials and expanding the participant pool to include older women.
The big news, according to those who studied flibanserin? "There is something that works on the neurotransmitters in the central nervous system to alter sexual desire in a positive way," says John M. Thorp Jr., MD, McAllister distinguished professor of obstetrics and gynecology at the University of North Carolina at Chapel Hill School of Medicine, and a principal investigator for the U.S. trials.
At the Congress, researchers reported the pooled results for 1,378 premenopausal women, average age 35, who took 100 milligrams of the drug or a placebo pill during a 24-week period. The trials were in Europe and North America. The women kept track of the number of satisfying sexual encounters -- defined as intercourse, oral sex, masturbation, or genital caressing by their partners. All women had to be in a stable, monogamous relationship. All women had a diagnosis of hypoactive sexual desire disorder (HSDD), marked by a decrease or absence of sexual desire accompanied by distress in the patient.
When researchers compared sexual desire and events during the last four weeks to the first four weeks, they found that those on the medication went from 2.8 sexually satisfying events in the first four weeks to 4.5 in the final four weeks. Those on placebo went from 2.7 to 3.7.
''The difference was [about] one additional satisfying sexual encounter a month," says Thorp.
The study also shows the drug improved sexual functioning and distress related to the sexual problems.
About 15% of the women taking the medication dropped out due to adverse events, according to information from Boehringer Ingelheim Pharmaceuticals, which makes the medications, while 7% of women on placebo discontinued the study. Among the most commonly reported side effects were daytime sleepiness, dizziness, anxiety, and fatigue.
How Flibanserin Works
Exactly how flibanserin improves sexual desire isn't known for sure. "We think it modulates neurotransmitters involved in sexual functioning," says Michael Sand, PhD, MPH, director of clinical research and team leader, flibanserin, for Boehringer Ingelheim.
''It interacts with [neurotransmitters] serotonin and dopamine in the central nervous system," Thorp says.
Originally studied as an antidepressant by Boehringer Ingelheim, the drug didn't prove effective for depression. But when researchers noticed reports of improved sexual desire in some participants, the research changed focus.
As for critics, Thorp acknowledges that ''there are multiple criticisms [of the studies] that are justifiable. One is the whole measurement issue and how do you quantify an objective response? That's particularly hard when the disorder is subjective."
He notes, too, that the placebo group also saw improvement. "There was a big placebo effect,'' he says, noting that attention from a concerned doctor may also contribute to improvement in the sexual functioning of women with HSDD.
"The data look good," says Kathleen Segraves, PhD, associate professor of psychiatry at Case Western Reserve University in Cleveland and a sex therapist who reviewed the data for WebMD. "But only clinical experience and actual practice will reveal how clinically useful the effect is."
Case Western Reserve was one of the U.S. study sites for flibanserin, but Segraves was not involved in the study.
The real world, she says, is different from clinical trials. For instance, in the study, each woman kept an e-diary to assess her level of desire daily. That exercise may have kept women focused on the problem, Segraves says, and perhaps more motivated.
To call flibanserin the female Viagra, however, is incorrect, she says. "Viagra is a vasodilator. It only makes the penis hard, it doesn't work on the desire of a man. It may give him more confidence. It gives him a reliable erection. It inflates the penis. He still needs to have desire."
The differences in the number of satisfying sexual encounters may seem small, Segraves says. But it would probably not be considered small by the women who have the condition, she says.
"You have to remember these women have lost desire over time and for some time. You have to remember these women [with no sexual desire] are very distressed by it. If you go from zero to one, you're pleased as punch, because you were flat-lining before."
Some wonder if developing a pharmaceutical for women’s lagging desire is more about business than pleasure. "We need to address multiple factors that underlie sexual desire," says Gina Ogden, PhD, a sex therapist in Cambridge, Mass., and author of The Return of Desire. Of the development of flibanserin, she says: "I think the focus is more to line the pockets of the pharmaceutical companies than to address the real and multiple factors involved in women's sexual desire." A woman's desire, says Ogden, is influenced by many factors, including her feelings about sex, what sex means to her, and what types of intimacy she prefers.
Boehringer Ingelheim is continuing studies. Recruitment of both premenopausal and postmenopausal women with HSDD for new clinical trials is beginning, Sand says.
He wouldn't comment on a possible timeline of when the drugmaker might ask for FDA approval or when it may be on the market.