Ever since Viagra met blockbuster success in 1998, the drug industry has sought a similar pill for women.

Now, a German drug giant says it has stumbled upon such a pill and is trying to persuade the U.S. Food and Drug Administration that its drug can help restore a depressed female sex drive. The effort has set off a debate over what constitutes a normal range of sexual desire among women, with critics saying the company is trying to turn a low libido into a medical pathology.

On June 16, an FDA staff report recommended against approving the drug, saying the maker, Boehringer Ingelheim, had not made its case and that the benefits of the daily pill did not outweigh its side effects, which included dizziness, nausea and fatigue.

That staff report came ahead of a meeting by an FDA advisory panel of experts who are to vote on whether to recommend that the agency approve the pill, which would be the first drug aimed specifically at a low sex drive in premenopausal women.

FDA staff reports carry weight but do not always sway how advisory panels vote, and advisory votes do not always predict what the FDA might finally decide.

Some analysts forecast that if the drug does reach the market, it could have annual sales in this country of $2 billion – or about equal to the current combined annual U.S. sales of the men’s drugs Viagra, Levitra and Cialis.

In the past month, Boehringer has been trying to lay the consumer groundwork with a promotional campaign about women’s low libido, including a website, a Twitter feed, a Discovery Channel documentary and a publicity tour by Lisa Rinna, a soap opera star and former Playboy model, who describes herself as someone who has suffered from a disorder that Boehringer refers to as a form of “female sexual dysfunction.”

There is no dispute that some women have a depressed level of sexual desire that causes them anguish. Boehringer cites a condition – hypoactive sexual desire disorder – that is included in the Diagnostic and Statistical Manual of Mental Disorders, a reference book for psychiatrists and insurers.

But many experts say that unlike sexual dysfunction in men – which has an obvious physical component – sexual problems in women are much harder to diagnose. And among doctors and researchers, there is serious medical debate over whether female sexual problems are treatable with drugs. Some doctors advocate psychotherapy or counselling, while others have prescribed hormonal drugs approved for other uses.

“It’s a dicey, difficult problem,” says Dr. Jeffrey T. Jensen, a medical professor and director of Women’s Health Research Unit at the Oregon Health Sciences University.

Critics say Boehringer’s market campaign exaggerates the prevalence of the condition and could create anxiety among women, making them think they have a condition that requires medical treatment.

“This is really a classic case of disease branding,” said Adriane Fugh-Berman, an associate professor at Georgetown University’s medical school who researches drug marketing and has studied the campaign. “The messages are aimed at medicalizing normal conditions and also preying on the insecurity of both the clinician and the patient.”

Boehringer developed the drug, flibanserin, as an antidepressant, but it failed to lift depression. The company says it learned serendipitously that the pill, taken daily for weeks, could restore female libido.

Peter J. Piliero, Boehringer’s director of medical affairs in the United States, says the lack of libido to the point of distress is a serious problem for some women.

“This is a real disease,” Piliero said in an interview. “There’s an unmet medical need among premenopausal women to have a treatment.”

Boehringer says the drug reduces the brain chemical serotonin, which can blunt sexual desire, and increases dopamine and norepinephrin, which improve desire, he said. By acting on a woman’s brain, it takes a different approach from hormonal drugs or the action of Viagra for men, which increases blood flow.

Boehringer’s application for FDA approval said that its two key 24-month studies, of 1,323 premenopausal women who said they suffered distress over lack of libido, had found small but statistically significant improvements. The FDA staff report, though, said that Boehringer’s data had not sufficiently demonstrated a second criteria the agency had set for approving such a drug – specifically, that women also report an increased level of sexual desire. The FDA required daily self-reporting by the women in the studies; Boehringer said it had provided monthly reports.

Leonore Tiefer a psychologist and professor at New York University who has researched the topic of female sexual desire for more than a decade and plans to testify to the FDA panel, said Boehringer had gone too far with its publicity effort.

She said that if the drug were approved, she worried that “the much larger group of women without any medical reason for their sexual distress will inevitably be misinformed and misled into thinking that there is a pill that can get them the sex life they read about, the one they think everyone else is having.”