For the first time, the U.S. Food and Drug Administration has given its blessing to a prescription drug intended to increase sexual desire in women.

The FDA's green light on the drug flibanserin, often known by the nickname "pink Viagra," reverses two earlier decisions to reject the medication as a treatment for hypoactive sexual desire disorder.

The approval of flibanserin, which will be marketed as Addyi, offers women distressed by their low sex drive a once-a-day salmon-colored pill. Clinical trials presented to the FDA showed that compared with pre-menopausal women who got a placebo, those who took flibanserin reported a modest but measurable rise in sexual desire and increased their number of “sexually satisfying encounters” by roughly one per month, from a median of two to three to between 2 1/2 and four.

In tests, the most common side effects of the drug included dizziness, sleepiness, nausea and fatigue. Addyi should be taken at bedtime to reduce these risks, the FDA said.

Researchers estimate that about 8.3% of women between 30 and 70 in the United States suffer distress from lack of sexual desire. The condition, only recently deemed a medical disorder, appears to peak between the ages of 40 and 60.

Though many of those women may seek prescriptions for Addyi, the FDA said the drug could be marketed as safe and effective only for patients who had not yet reached menopause. For most women, that happens when they are in their late 40s or early 50s. However, once a drug wins FDA approval, doctors are free toprescribe it to patients as they see fit.

Addyi acts to increase the activity of the neurochemical serotonin in the brain. It was initially developed as an antidepressant, then abandoned by the German drug company Boehringer Ingelheim for lack of effectiveness. The mechanism by which the drug improves female sexual desire — a hugely complex confluence of hormones, mood, circumstance and physiology — is not known.

Sprout Pharmaceuticals, which bought the rights to flibanserin in 2011, said it planned to make Addyi available to patients starting in mid-October. Gynecologists are expected to be the main prescribers, but it could also by offered by primary care physicians and mental health professionals who specialize in sexual health.

Cindy Whitehead, chief executive of the Raleigh, N.C., company, said Addyi would be priced so that women with insurance coverage could get a one-month supply with a copayment of between $30 and $75 per month. That would make the drug as financially accessible to women as most erectile dysfunction drugs are to men, she said.