The pink pill German drug firm Boehringer Ingelheim is trying to market in the United States as a libido-booster for women produced inconclusive results in two clinical trials, the Food and Drug Administration (FDA) said Wednesday.

Originally intended as an anti-depressant, the drug flibanserin - in the form of a pink pill - began being tested years ago as a potential libido aid after women said it failed to fight the blues but did boost their sex drive.

Lack of desire is the most common sexual problem in women aged 30 to 60, just as erectile dysfunction is the most common sexual disorder among men in the same age bracket, researchers said.

Clinical trials to test flibanserin's efficacy in raising the level of sexual desire in women were held in Canada, Europe and the United States.

The results of two US trials with the drug and a placebo were published on the FDA's website: "both failed to demonstrate a statistically significant improvement on the co-primary endpoint of sexual desire," said the FDA.

"Therefore, 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 administration added.

Besides the inconclusive results, the FDA noted the drug in some patients caused side effects including depression and dizzyness.

The FDA said its is waiting for recommendations on the little pink pill from an independent panel of experts due to report on Friday. The administration is not legally bound to comply with the advice, but usually does.

Boehringer Ingelhein has been researching flibanserin as a treatment for post-menopausal HSDD in women since the popular Viagra hit the market for male ED in 1998.

The potential market for a libido booster for women has been estimated by some analysts at around two billion dollars.

Medical research has found that 40 percent of women suffer from different degrees of HSDD.

Flibanserin belongs to a family of anti-depressants that acts on the body's level of serotonin, a molecule that plays a role in mood changes.