Women may experience small benefits with a drug approved last year in the U.S. to treat low sexual desire in women, but at a high risk of experiencing unpleasant side effects, according to a new analysis.

The findings "suggest that the benefits of flibanserin are marginal," given that "one in three women experience side effects, of which the most common ones include dizziness, sleepiness, nausea, and tiredness," said lead author Dr. Loes Jaspers, of Erasmus University Medical Center in Rotterdam, the Netherlands.

Flibanserin, marketed by Valeant as Addyi, was approved by the U.S. Food and Drug Administration (FDA) in 2015 to treat premenopausal women with hypoactive sexual desire disorder (HSDD).

Writing in JAMA Internal Medicine, Jaspers and her colleagues say HSDD affects 10 to 40 percent of women. It's defined as a lack of desire or fantasies for sexual activity that isn't caused by factors like medication, mental disorders or relationship stress.

Sometimes called the "female Viagra," flibanserin works by affecting brain receptors to increase sexual arousal in women. Pfizer's Viagra, also known as sildenafil citrate, treats a physical condition when men are already aroused.

Flibanserin was approved by the FDA on its third attempt, but the agency's clinical reviewers recommended that it be rejected, wrote Drs. Steven Woloshin and Lisa Schwartz, of The Dartmouth Institute for Health Policy and Clinical Practice in Lebanon, New Hampshire, in an editorial.

They note that the drug comes with a so-called black-box warning - the FDA's strongest - that women may suffer severe low blood pressure or faint if they take the drug with alcohol, certain medications or have liver problems.

Jaspers' team analyzed data from five published and three unpublished randomized trials including nearly 6,000 women. Women who took flibanserin generally took 100 milligrams daily before bed.

Women taking flibanserin had about one-half of one more satisfying sexual encounter per month, compared to women taking a placebo or "dummy" pill, the research showed.

Women taking flibanserin were also about four times more likely to experience dizziness and sleepiness, more than twice as likely to experience nausea and about 60 percent more likely to experience fatigue.

In a statement to Reuters Health, Dr. Tage Ramakrishna, Valeant's chief medical officer and president of research and development and quality, said the study confirmed the findings of the trials used to obtain FDA approval. Also, Ramakrishna said, analyses of existing data carry less weight than the trials FDA reviewed.

"It is crucial that women suffering from HSDD are able to speak to their physicians about the full range of options - including medical treatment - to manage this serious and well-established condition," said Ramakrishna. "Analyses such as the one published in JAMA Internal Medicine, by omitting context and downplaying the importance of increased sexually satisfying events to those with HSDD, makes that conversation more difficult."

Jaspers said their findings suggest the FDA should reconsider its approval of flibanserin but cautioned that the agency may have taken other factors into account to make its decision.

"It could be that at the time of approval they thought the level of evidence was higher than what was found in our study," she told Reuters Health by email. "Also, they may have taken into consideration other aspects in their decision making, that were not covered in this review and meta-analysis."

Woloshin said the FDA requested additional studies of the drug after its approval, which may be important for patients to know.

"It might change their enthusiasm of the drug," he said.

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