Is sexual desire a human right? And are women entitled to a little pink pill to help them feel it?

Those questions are being raised in a campaign that is pressing the Food and Drug Administration to approve a pill aimed at restoring lost libido in women. The campaign, backed by the drug’s developer and some women’s groups, accuses the F.D.A. of gender bias for approving Viagra and 25 other drugs to help men have sex, but none for women.

“Women have waited long enough,” the effort, known as Even the Score, says in an online petition that has gathered more than 40,000 signatures. “In 2015, gender equality should be the standard when it comes to access to treatments for sexual dysfunction.”

The drug, flibanserin, has been rejected twice by the F.D.A. on the grounds that its very modest effectiveness was outweighed by side effects like sleepiness, dizziness and nausea. The first rejection, in 2010, followed a decision by a committee of outside advisers to the agency who unanimously opposed approval.

Barbara Gattuso, 66, with her husband, Gregg, 67, in Boston last week, on vacation from their home in San Diego. “I was the one initiating sex, much to the surprise of my husband,” Ms. Gattuso said at the F.D.A. workshop in October.

On Thursday, F.D.A. advisers will once again consider whether flibanserin should be approved.

Sprout Pharmaceuticals, which now owns the drug, has submitted new data, including a study to demonstrate that the pill does not impair driving. Still, approval might hinge on whether the F.D.A. agrees to interpret the old data in a new way and whether the politics of such drugs has changed.

Even the Score is backed by, among others, the National Council of Women’s Organizations, the Black Women’s Health Imperative, Jewish Women International and some medical groups like the Association of Reproductive Health Professionals. It has persuaded some members of Congress to write to the F.D.A. and has also created a wicked spoof of a Viagra commercial.

A spokeswoman for the F.D.A. said the agency “strongly rejects claims of gender bias.” She said that in 2012 the agency identified female sexual dysfunction as a priority and held a two-day public workshop on drug development for the condition in October.

But the path to a drug for women’s sexual dysfunction has been difficult. Pfizer gave up testing Viagra for women in 2004, the same year an F.D.A. advisory committee voted against a testosterone skin patch for women developed by Procter & Gamble. A testosterone gel for women being developed by BioSante failed in clinical trials in 2011.

Some other women’s groups, including the National Women’s Health Network and Our Bodies Ourselves, say that Even the Score is making a mockery of the drug approval process under the guise of women’s rights.

“I don’t think there is anything sexist about denying approval for drugs that don’t have an adequate risk-to-benefit ratio,” said Thea Cacchioni, an assistant professor of women’s studies at the University of Victoria in British Columbia, who is writing a book about the issue called “Big Pharma, Women, and the Labor of Love.”

Leonore Tiefer, a psychologist at the New York University School of Medicine, said Sprout and its allies were trying to make low desire into a medical problem treatable by drugs when “most of these problems are psychological or relational.”

Lack of spontaneous desire, she said, is not necessarily a problem in itself. The American Psychiatric Association no longer lists hypoactive sexual desire disorder, the condition flibanserin is designed to treat, in its manual of mental health disorders. Low desire is now combined with low arousal in a broader diagnosis on the grounds that some women do not feel desire until they are aroused.

Even the Score does exaggerate somewhat. Most of the 26 drugs for men are different formulations of the same substance, testosterone. And none are approved to treat low sexual desire, though that can be one symptom of testosterone deficiency. Viagra improves blood flow to the penis needed for an erection. For women, estrogens and a drug called ospemifene have been approved to treat pain during intercourse that can occur after menopause.

Still, even many members of the F.D.A. advisory committee that rejected flibanserin in 2010 acknowledged then that lack of desire was a genuine condition and that drugs should be developed for it.

Some sexual medicine experts say the condition causes emotional distress and interferes with relationships.

“Our usual patient is someone who is fearful of losing the relationship they have been in for years,” said Dr. Irwin Goldstein, director of sexual medicine at Alvarado Hospital in San Diego and a consultant to many drug companies. “It’s tragedy after tragedy after tragedy.”

One of his patients, Jodi Cole, 33, of Porter, Okla., said her lack of desire “tends to cloud my thoughts of everything related to my husband.” She said that “replacing the dread I have for intimacy with desire would be life-changing.”

About 10 percent of American women suffer from a lack of desire that causes distress, according to a survey conducted by an academic researcher but financed by Boehringer Ingelheim, the original developer of flibanserin. The drug, taken daily, would be for premenopausal women whose loss of desire was not from known causes like disease or the side effect of a drug.

Dr. Goldstein said it was gender bias to categorize male sexual dysfunction as a simple physical problem and women’s as complex, psychological and unamenable to drugs. He noted that antidepressants that increase the level of serotonin in the brain can have a side effect of decreasing libido. Flibanserin does the opposite — transiently decreasing serotonin while raising levels of two other neurotransmitters, dopamine and norepinephrine.

Susan Scanlan, chairwoman of Even the Score, said the side effects of flibanserin, like sleepiness and dizziness, were not so serious. By contrast, she said, Viagra and some other drugs for men can cause blindness, penile rupture and other serious side effects.

“The implication is that men can be trusted to make a rational decision of risk versus reward and women can’t,” she said.

Flibanserin appears to be safer and more effective than 1,000 other already-approved drugs. 

Ms. Scanlan said Even the Score was brought together by Audrey Sheppard, who once headed the office of women’s health at the F.D.A. and was retained as a consultant by Sprout.

Ms. Sheppard said she introduced Cindy Whitehead, Sprout’s co-founder and now chief executive, to Washington activists on women’s rights in 2013, when it looked like the drug might be approved. After it was rejected a second time and a meeting with the F.D.A. incensed the advocates, the campaign started “in a spontaneous combustion kind of way.”

Much of the coalition’s activities are run by a public relations company, Blue Engine Message and Media. Officials declined to discuss the budget and how much is paid for by Sprout and two other companies developing drugs for female sexual dysfunction — Palatin Technologies and Trimel Pharmaceuticals.

One participant in the coalition, the International Society for the Study of Women’s Sexual Health, urged its members to recruit their patients suffering from low libido to testify at the public workshop in October, saying that money would be available to pay for transportation. A spokeswoman for Even the Score said the coalition provided that money.

Boehringer Ingelheim gave up on flibanserin after the first F.D.A. rejection in 2010. Cindy and Robert Whitehead, a couple running a company that made a testosterone product for men, started Sprout to acquire flibanserin. Based in Raleigh, N.C., and privately held, Sprout has raised $50 million, Ms. Whitehead said.

Judging how effective a drug is can be difficult. In one clinical trial, women taking flibanserin reported having an average of 4.4 “satisfying sexual experiences” a month, compared to 3.7 for women getting a placebo and 2.7 before the study began. While the difference between the drug and placebo of a little less than one event a month was statistically significant, there was debate at the 2010 advisory meeting on whether it was meaningful.

But the drug was not significantly better than the placebo in raising desire, as recorded in a daily diary.

Still, more women on the drug than on the placebo said they had experienced less distress and a meaningful change. And some women have said the drug had a big effect.

“I was the one initiating sex, much to the surprise of my husband,” Barbara Gattuso of San Diego said at the F.D.A. workshop in October. Ms. Gattuso, who said she had had low desire for 25 years, said she was “devastated” when the trial ended.

At the workshop, some sexual medicine experts said the best measure of a drug would be a monthly questionnaire asking about their desire levels.

Dr. James A. Simon, a clinical professor of obstetrics and gynecology at George Washington University and an investigator in flibanserin clinical trials, said in an interview that the number of sexually satisfying events depended on a woman’s partner, so it was not a true measure of desire. And some women got annoyed at being asked to rate their level of desire every single day. The monthly questionnaire, he said, gauged “the gestalt of the overall.”

Using the monthly questionnaire, flibanserin beat placebo in most trials. If the F.D.A. accepts that measure, the drug could win approval.