A drug to boost female sex drive could be worth billions to the company that manages to get it approved by the Food and Drug Administration. Recently, two new treatments have made strides towards that goal. ­­­But some are skeptical of the real value of such a drug to the women it's supposed to help.

In late 2004, FDA approval of Intrinsa, a testosterone patch for low female sex drive, seemed imminent. News reports heralded Intrinsa as a "Viagra for her," suggesting that it would revolutionize sexual health for women just as erectile dysfunction pills had for men.

Except an FDA advisory panel saw things differently. Finding numerous problems with the evidence for the drug's effectiveness and safety, experts on the panel voted against approving it. Procter & Gamble, the company responsible for Intrinsa, withdrew its application. Procter & Gamble is a WebMD sponsor.

Now the frontrunner in the race to market the first prescription drug for low female sex drive is Boehringher-Ingelheim Pharmaceuticals. It has a drug called flibanserin in phase III clinical trials, the final phase of drug testing required for FDA approval. The company is a WebMD sponsor.

Flibanserin is a bit mysterious. It is a kind of antidepressant, but it hasn't been approved previously for any use. Boehringher-Ingelheim is saying little publicly about the drug. The company declined WebMD's request to interview a company representative, instead issuing a prepared statement. The statement does not explain how the drug is supposed to work, other than that "flibanserin is a molecule acting on the central nervous system and is not a hormone product."

Another drug, called bremelanotide, is in development for low female sex drive and male erectile dysfunction at the same time. Both potential uses are being tested in phase II clinical trials, which are early studies to assess how well a drug works and how safe it is.

Bremelanotide is a new chemical created in the laboratory. It's given in the form of a nasal spray, and it acts on the central nervous system.

"It's actually working in a region of the brain called the hypothalamus, which is known to be involved in sexual arousal in both men and women," says Carl Spana, PhD, CEO of Palatin Technologies, the company researching bremelanotide.

What Is Desire?

Arousal -- that is, erection -- is the goal of treatment for men. For women, researchers hope that ease of arousal will translate to increased sexual desire.

Technically, arousal and desire are not the same thing. Arousal is the physical and psychological state of being primed for sex. The penis becomes erect, the vagina lubricates, heart rate increases, and blood vessels dilate. Whereas arousal can be easily seen, sexual desire is vague. It has to do with wanting to become aroused, but there are a lot of questions about what that really means.

Not everyone thinks that sexual desire is a medical issue. Lenore Tiefer, PhD, a psychologist at the New York University School of Medicine, is an outspoken critic of what she sees as a trend toward unnecessary medical intervention in sex. She is a founding member of a group promoting "A New View of Women's Sexual Problems," and editor of a book by that title.

The idea that desire is a thing women have or lack, apart from any object of desire, is mistaken, she says. But it is convenient for the purpose of selling pharmaceuticals.

"I don't think people desire sex, or rather, let's put it this way: They're learning to desire sex," she tells WebMD. "It used to be I thought that people desired people: 'I desire Fred' or 'I desire Louise.' Then there was masturbation, which was a kind of tension-relieving thing where you felt like having an orgasm, but it wasn't sexual desire. It wasn't anything like that. Sexual desire was this longing that you felt in your body or in your heart to be with that person over there."

Tiefer contends that there are too many other reasons why desire for sex might wane to pin it on a biological cause. Fred is emotionally distant and snappish. Louise feels bad about how her body looks. Early in her life she learned that sex is dangerous and yucky. At the end of the day, after the kids are tucked in and dinner dishes are washed and put away, she has only enough time to catch a few minutes of American Idol before lights out.

Another prominent sex researcher, Rosemary Basson, MD, of the University of British Columbia, Canada, agrees that the medical focus on desire is misplaced. Women and men "have multiple motivations to be sexual, and 'desire' -- as in urging 'lust,' 'horniness,' or 'drive' -- is only one of these reasons," she tells WebMD. Desire for sex can also be the desire to feel emotional closeness with someone, to please that person, or to feel attractive.

She points out that the definition of this "mental disorder" assumes that all women have a constant amount of sexual desire that is normal, like the pilot light of a stove. Just turn up the gas, and you're cooking. But there's no definition for what a normal level of desire is, so no one can say what's "low," Basson says.

Sometimes when the motive to have sex is something other than a physical drive, some women just can't get into it. "Even if she is trying to focus on any pleasurable feelings, her body is simply not responding and neither does her mind," Basson says. "It stands to reason that her motivation will sooner or later also drop." That's where she thinks medicine can help. It also happens to be the approach of researchers studying the drug bremelanotide.

Michael A. Perelman, PhD, is a consultant involved in the clinical trials on bremelanotide and co-director of the Human Sexuality Program at Presbyterian Hospital and Weil-Cornell Medical School in New York City. He explains how the drug might work in terms of setting the "tipping point" for sexual arousal lower. He thinks the drug should be used together with counseling to help with emotional problems that inhibit desire.

"I'm interested in helping people respond more to the right kind of stimulation from the right person when that's just not happening naturally for them, in the way that they would like, or that it used to," he says.

The Market for Desire

If one of these drugs eventually wins approval, the drugmaker probably spend millions to advertise it. it's hard to imagine that it would be discretely recommended by licensed sex therapists as part of a comprehensive approach to women's sexual problems. Instead, ads will urge women to "ask your doctor if it's right for you."

Millions may go ahead and do that.

"I think it's impossible that it won't sell a lot," Tiefer says. "I don't see any way around it."

The size of the potential market for these drugs is debatable because estimates of how many women could be diagnosed with the disorder vary widely. Would you believe up to 43% of women have low sexual desire? That figure comes from a survey published in the January/February 2005 issue of the International Journal of Impotence Research. It got a lot of play in the early publicity for Intrinsa, and it is still cited often. Those offering it as evidence of a vast epidemic have been sharply criticized, however. The survey from which it came asked women if they ever lacked interest in sex but not whether it caused them any distress. The survey also found that lack of interest in sex was linked to age and depression.

Other research has come up with different numbers. Survey results published in 2003 in the British Medical Journal show that about 10% of English women reported "lack of interest in sex" lasting at least six months in the past year.

A survey by John Bancroft, PhD, former director of the Kinsey Institute, published in the Archives of Sexual Behavior in 2003, asked women not only if they lacked interest in sex, but also if it caused them distress personally or if it caused distress in their relationship. About 7% of the women reported having "no sexual thoughts" in the past month, but less than 3% said they didn't think about sex and felt distress because of it.

On the one hand, it's probably not true that nearly half of all women have sexual dysfunction. But on the other hand, sexual problems are not wholly invented by the pharmaceutical industry.

"It's really important to recognize that people really do suffer," says Lisa Schwartz, MD, a professor at Dartmouth Medical School in Hanover, N.H., who researches harms vs. benefits in medical treatment. "It's just a question about what the solution to that suffering is, how to acknowledge that suffering in a way that's helpful -- and it's not necessarily by putting it in the medical care system."

Peer Pressure

It's not farfetched to suppose that if Fred wants it more often than Louise does, he might pester her to ask her doctor about that drug in the ad on TV until she finally caves in.

If a drug for female sex drive were successful, women might feel pressure to conform to a new cultural norm. "People do now expect things that they didn't used to," Tiefer says. Take orgasms, for instance. Orgasms are divine and everyone is entitled to be as orgasmic as possible. But the ideal of being able to have routine or multiple orgasms sets up some women to feel defective if they don't. Men, too, are expected to be able to get erections no matter what. Today it would strike many people as plain weird that a man might choose to live with erectile dysfunction. Ten years ago it wouldn't have.

Louanne Cole Weston, PhD, WebMD's Sex Matters® columnist, says she thinks there has been too much hand-wringing over these kinds of questions. "I don't want to belittle women by saying, 'We're not going to give you this drug' or 'we're not going to look into this drug because we don't think you're capable of standing up to the pressures of the people in your life,'" she says.

If libido drugs don't do anything for women, despite marketing efforts, they won't take them, she argues. But she hopes that someday something that works will make it to the market and help a lot of people.

When and what that is will ultimately come down to what the studies on flibanserin and bremelanotide show and how the FDA evaluates the science. "It all depends on how scientifically rigorous they're going to be," Tiefer says.

Click here to read more: A Woman's Guide to Reviving Sex Drive