Updated from 5:21 p.m. EDT

An advisory committee of the Food and Drug Administration said Thursday that an experimental drug to increase women's sexual desire will need more study of its long-term safety before the panel could recommend approval.

The panel voted unanimously that the FDA should reject the product.

The committee of experts said that although the drug Intrinsa, a transdermal patch that transmits the hormone testosterone, is effective, the company's developer hadn't provided enough information about the drug's long-term safety. The drug is made by Procter & Gamble ( PG), under license from Watson Pharmaceuticals ( WPI).

Many Wall Street analysts had speculated that Intrinsa could be the female version of Viagra, the erectile dysfunction drug made by Pfizer ( PFE).

P&G was asking the advisory committee to approve the drug designed to improve sexual desire in menopausal women whose ovaries have been surgically removed. The FDA isn't bound by its advisory committees' opinions, but the agency usually follows their recommendations.

Intrinsa would be the first FDA-approved drug to treat the condition called hypoactive sexual desire disorder. Other companies are working on female sexual disorder products such as patches, pills, gels, creams and nasal sprays.

The decision is a setback not only to P&G and to Watson but also to a host of other companies that are working on drugs to treat diminished sexual desire in women. The advisory panel's announcement came after markets had closed.

P&G's stock closed up $1.16, or 2.1%, to $55.82 in regular trading. But it gave back 71 cents, or 1.3%, in after-hours trading. Watson's stock closed at $29.30, gaining 23 cents, or 0.8%, in regular trading.

The biggest loser was BioSante Pharmaceuticals ( BPA), which is developing a testosterone gel. In regular trading, the company's stock lost 90 cents, or 10.7%, to $7.50. In after-hours trading, the stock was beaten down by $2.50, or 33.3%, to $5.

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