A once-daily pill developed by Germany's Boehringer Ingelheim increased female sex drive in late-stage trials, putting the group in the frame to launch the first non-hormonal treatment for women with low libido.

The compound known as flibanserin promoted sexual desire and increased the number of "satisfying sexual events" in women suffering from abnormally low libido, Boehringer said on Monday.

The results of four Phase III studies involving more than 2,000 pre-menopausal woman suffering from so-called Hypoactive Sexual Desire Disorder (HSDD) were presented at the congress of the European Society for Sexual Medicine in Lyon, France.

Unlike Procter & Gamble's hormone patch Intrinsa, targeted at woman after the menopause, flibanserin directly manipulates the chain of chemical reactions in the brain believed to trigger sexual desire.

"By modulating the neurotransmitter system, flibanserin may help to restore a balance between inhibitory and excitatory factors leading to a healthy sexual response," said Elaine Jolly, a Canadian gynecologist and medical researcher who helped oversee the trials.

Boehringer Chief Executive Andreas Barner told German magazine WirtschaftsWoche in July that flibanserin could come to market in two to three years.

A spokeswomen for Boehringer, Germany's second-largest drugmaker after Bayer, said the company was preparing regulatory filings in the United States and subsequently for Europe and other markets.

She declined to provide a timeframe for filings and market launch and said Boehringer would not publish an assessment for the drug's annual peak sales potential.

HSDD is defined as a lack of sex drive irrespective of partner or situation in otherwise healthy women.

Male impotence pills such as Pfizer's Viagra, Eli Lilly's Cialis and Bayer's Levitra, which widen blood vessels to increase the blood flow needed for an erection, have failed to show notable aphrodisiac effects in women.

During the half-year course of once-daily flibanserin in the trials, the number of satisfying sexual events — which did not necessarily involve orgasm — rose to an average 4.5 per month from 2.8 in the North American arm of the trial, the study shows.

In the control group on placebo the rate rose to 3.7.

Women on the drug also reported a higher level of sexual desire and less distress from sexual dysfunction than those on placebo.

The drug's side effects were described as mild to moderate and included dizziness, nausea, sleepiness and insomnia.

This prompted about one in seven participants on flibanserin to drop out of the therapy, while the drop-out rate was roughly one in 14 in the placebo group, the data show.

Procter & Gamble's Intrinsa testosterone patches are licensed for use in Europe but not in the U.S., where regulators voted in 2004 against approving the patches that deliver the male hormone, citing lack of evidence for their long-term safety.

U.S. specialty drug company BioSante, which is developing a testosterone skin gel to treat a decline in libido in menopausal women, has said the market for treatment of female sexual dysfunction in the U.S. was worth more than $2 billion in annual sales.

Boehringer cited studies saying one in 10 U.S. women complained of low sexual desire, which may be due to HSDD.