An advisory panel for the US Food and Drug Administration Friday voted unanimously against approving a pill that helps boost women's sex drive, described by some as the "female Viagra."
The FDA's Reproductive Health Drugs Advisory Committee said the evidence presented had not demonstrated the effectiveness or safety of flibanserin, made by the German company Boehringer Ingelhein.
"The efficacy was not sufficiently robust to justify the risks," said panel chair Julia Johnson, chief of obstetrics and gynecology at the University of Massachusetts Medical School, after the committee's deliberations.
The FDA usually follows these panels' advice, even though it is not required to do so by law.
Flibanserin, the latest effort to come up with a female counterpart to the wildly popular male erectile dysfunction pill Viagra, works on brain chemicals to treat pre-menopausal women with a low sex drive, according to the maker.
To date, the drug known by the commercial name Girosa has not been approved for sale in any country, in contrast to treatments for male sexual dysfunction.
Pharmaceutical firms have vied for a spot in this potential market estimated to be worth two billion dollars since Viagra was launched in 1998 becoming a huge success, and was subsequently followed by competitors Cialis and Levitra.
Several medical trials, including a study published in the New England Journal of Medicine, say that at least 40 percent of women suffer from varying degrees of sexual hypoactivity, though critics warn that big pharma has funded a number of these surveys.
An analysis of the two clinical trials published on the FDA's website note that both "failed to demonstrate a statistically significant improvement" in sexual desire, even though patients who took flibanserin had slightly more satisfying sexual relations with their partners than those who took a placebo.
"Neither study met the agreed-upon criteria for success in establishing the efficacy of flibanserin for the treatment of HSDD" (Hypoactive Sexual Desire Disorder), the report added.
The two-year studies, measured by women's diary entries in the United States and Canada, found that women who took flibanserin reported an average 4.5 more satisfying sexual experiences per month, versus 3.7 for those who took a placebo.
The women -- most of them married with a high education and good health apart from their decreased libido -- had reported an average 2.8 satisfying experiences before taking the medicine.
According to the studies cited by FDA, flibanserin can also cause side effects such as depression or dizziness.
Flibanserin belongs to a family of anti-depressants that reduce the level of serotonin, which has an effect on mood and can put a damper on sexual desire.
The drug also controls the levels of dopamine and norepinephrine in the blood, substances that act on sexual desire, the pill's manufacturer said.