German drugmaker Boehringer Ingelheim didn't set out to create a Viagra-like drug for women. The company was simply trying to develop a fast-acting antidepressant, one that patients would respond to in a matter of days, not weeks like most current treatments. By the late 1990s the company had developed a molecule called flibanserin that seemed to relieve stress in rats. But like many promising drugs, it flopped in human trials. Says Dr. Lutz Hilbrich, the company's executive director of general medicine: "We did not see the effect we were expecting."
But what they did see surprised them. Like all companies working on antidepressants, Boehringer surveyed patients in its clinical trial to assess dampening of libido, a well-established side effect. Far from complaining about a drop in sexual desire and arousal, many of the women in the trial reported a surge. The men had no such response—and neither group showed any improvement in mood. "It is an interesting drug," says Dr. André T. Guay, director of the Center for Sexual Function at the Lahey Clinic Northshore, Peabody, Mass., and assistant professor at Harvard Medical School. "These things come about in strange ways."
It's hard to escape a comparison with Viagra. In the mid-1990s, researchers at Pfizer Inc. (PFE ) were testing an experimental drug for angina, or chest pain, and were stunned to discover the stimulating side effect. Since Viagra hit the market in 1998, drugmakers have been searching for the female equivalent. Procter & Gamble (PG ), for instance, is trying to win Food & Drug Administration approval for a testosterone patch that produces modest effects in women, and others are testing topical creams and nasal sprays. "It is a very large potential market for drug companies," says Cleveland Clinic urologist Dr. Jeffrey S. Palmer. Annual sales of erectile dysfunction drugs for men have already topped $2 billion.
Boehringer has placed a big bet on flibanserin. The company has launched four major clinical trials, involving 5,000 women in 220 locations, with the goal of applying for FDA approval in 2009.
Drug development is never easy, however, and flibanserin faces a tougher road than usual. There's an ongoing controversy about whether or not a female analog to erectile dysfunction even exists. In October, the Endocrine Society issued guidelines cautioning that sexual dysfunction, if it exists at all, may have nothing to do with any "defect in the woman's physical sexual response system." The Society concluded that the most common current treatment, testosterone, should not be recommended. The big question: If a woman doesn't experience physical desire, is it a medical condition, like inadequate blood flow in men, or something purely psychological? "Maybe she just doesn't like the guy she's with," says Washington (D.C.) psychotherapist David Waldman.
NOT SO FAST
Plus, it's not yet clear exactly how flibanserin works. Company researchers have figured out that it hits several circuits in the brain that are linked to feelings and pleasure. One of those circuits apparently helps control sexual desire and arousal, although the effects are not immediate. "This is not something that can be taken on a Friday for the weekend," says Boehringer Ingelheim spokesman Mark R. Vincent. "There is a gradual increase in sexual desire over a six-to eight-week period."
Pinning down the mechanism is especially critical, in this case, because the fda views drugs that affect the complicated central nervous system with extra caution. Regulators are especially wary of drugs that might be used widely as a lifestyle choice rather than just to treat disease. "It is difficult for drugs for the central nervous system to be approved for something as banal as sexual function," says Lahey Clinic's Guay.
Doctors investigating new treatments for women retort that men's problems were also seen as largely psychological until Viagra came along, and that loss of sexual desire isn't trivial to many of those who experience it. Indeed, Boehringer says it's having no trouble recruiting women for the trial, some of whom travel long distances for the chance to try the drug. Even if flibanserin doesn't pan out, understanding how it boosts desire should point the way to better versions—and perhaps give women a choice about whether or not to pop a little pill.
By John Carey