A pink sex pill offered little help to women and came with unacceptable risks, US government advisers agreed on Friday, another setback in the search for a drug to boost female libido.

German drugmaker Boehringer Ingelheim failed to convince an expert panel that its pill increased sexual desire enough to win approval. "The efficacy was not sufficiently robust to justify the risks," said Dr Julia Johnson, the panel's chairwoman and head of obstetrics and gynecology at the University of Massachusetts Medical School.   

Women reported depression, fainting, fatigue and other problems in company studies of the drug known chemically as flibanserin.

The once-a-day pill, taken at bedtime, is the latest attempt to find a female counterpart to Pfizer Inc's Viagra, the blockbuster blue pill for men.

Drugmakers have been searching for a medicine to improve women's sex lives since Viagra successfully debuted 12 years ago. The market for a "pink Viagra" could stretch into the billions of dollars.

But some doctors and advocates worry that pharmaceutical companies are playing on women's insecurities to convince them they need a pill to improve their sex lives.

"Low sexual desire is not a disease," said Leonore Tiefer, a clinical associate professor of psychiatry at New York University, reading to the advisers from a petition opposing approval of flibanserin.   

The Food and Drug Administration will make the final decision on whether to approve the pill and usually follows the advice of its advisory panels.   

Privately held Boehringer wants clearance to sell its pill by prescription for premenopausal women with a persistent, bothersome and unexplained lack of sex drive.

"Women deserve the option to choose a safe and effective pharmacological therapy for this distressing condition," said Dr Anita Clayton, a Boehringer consultant and psychiatry professor at the University of Virginia.   

The drug, originally developed as an antidepressant, is believed to act on brain chemicals thought to play a role in sexual response, the company said.   

But the advisory committee of seven women and four men voted 11-0 that the drug's risks and benefits were unacceptable and 10-1 that effectiveness data was lacking.   

FDA reviewers, speaking before the panel voted, said flibanserin failed to increase sexual desire as measured by women's daily diary entries in two company studies.   

Boehringer said another analysis, based on a survey of women's responses, showed a jump in sex drive and lower distress levels with the drug.   

Women also reported slightly more satisfying sexual experiences -- an average of 4.5 per month compared with 2.8 before taking the medicine. For placebo patients, the rate rose to 3.7 during the six-month studies.
 - Reuters