WASHINGTON (REUTERS) - A controversial drug to treat low sexual desire in women won approval from U.S. health regulators on Tuesday, but with a warning about potentially dangerous low blood pressure and fainting when taken with alcohol.

Moreover, the U.S. Food and Drug Administration said the first approved drug for the condition, to be sold under the brand name Addyi, will only be available through certified healthcare professionals and pharmacies due to its safety issues.

The FDA has twice rejected the drug, flibanserin, made by privately held Sprout Pharmaceuticals. Its latest decision comes after an advisory panel concluded in June it should be approved with strict measures in place to ensure patients are fully aware of the risks.

Shares of rival Palatin Technologies rose 29 percent to $1.21 in extended trade.

The drug has been nicknamed "female Viagra" in media reports, even though it does not work like Pfizer Inc's blockbuster Viagra pill for men that, in 1998, became the first approved drug for erectile dysfunction.

Flibanserin needs to be taken every day. Unlike Viagra, which affects blood flow to the genitals, flibanserin works on the brain. It is similar to a class of drugs known as selective serotonin reuptake inhibitors, or SSRI's, that include antidepressants such as Prozac.

Originally developed by Germany's Boehringer Ingelheim, flibanserin was first rejected by the FDA in 2010 after an advisory panel said the benefits did not outweigh the risks. Sprout acquired the drug, conducted additional studies and resubmitted the application. In 2013, the FDA rejected it again.

The rejection sparked a lobbying campaign by Sprout, aided by some women's groups who accused the FDA of gender bias because it had approved Viagra for men—a charge the FDA vigorously rejected.

Flibanserin is designed for premenopausal women whose lack of sexual desire causes distress. Women who took the drug in a clinical study had an increase of about 1.0 sexually satisfying event (SSE) per month compared with those taking a placebo. Advocates claim that increase is meaningful. Critics say the small benefit is outweighed by the drug’s risks.

Reporting by Toni Clarke in Washington; Editing by Bernard Orr)
Published Aug 19, 2015

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