Boehringer says the drug reduces the brain chemical serotonin, which can blunt sexual desire, and increases dopamine and norepinephrine, which improve desire, the company said. By acting on a woman’s brain, it takes a different approach from hormonal drugs or the action of Viagra for men, which increases blood flow.

Boehringer’s application for F.D.A. approval said that its two key 24-month studies, of 1,323 premenopausal women who said they suffered distress over lack of libido, had found small but statistically significant improvements. The women lived in the United States or Canada, were mostly married, well-educated and found to have the sexual desire disorder but were otherwise healthy.

In results reported last fall at a medical conference in Europe, the drug was found to increase self-reported “sexually satisfying events” to 4.5 a month on average. The reported events, which did not have to include orgasm, compared with 3.7 a month by women taking a placebo and 2.7 by those who did not take any pills.

The F.D.A. staff report on Wednesday, though, said that Boehringer’s data had not sufficiently demonstrated a second criterion the agency had set for approving such a drug — specifically, that women also report an increased level of sexual desire. The F.D.A. required daily self-reporting by the women in the studies; Boehringer said it had provided monthly reports.

Lara Crissey, a spokeswoman for Boehringer, declined to comment on the F.D.A. staff report.

Other drug companies that have sought a drug to elevate women’s sexual desire have included Pfizer, which spent several years trying to show that its drug Viagra could work for women as well as men. When Pfizer ended that research in 2004, it said in a news release that female sexual disorders resulted “from a broad range of medical and psychological conditions.”

Procter & Gamble sought F.D.A. approval for a skin patch to raise the testosterone levels of women who had had their uterus and ovaries removed, but it was rejected in 2004 because of possible links to breast cancer and cardiovascular disease. In 2006, though, European regulators, saying the testosterone patch appeared safe at low doses, approved that drug to treat depressed sexual desire in women whose uterus and ovaries had been surgically removed.