May 21, 2014 -- It’s called the “little pink pill,” a tiny tablet that could have a huge impact on treating female sexual dysfunction. If it’s approved, it would become the first drug of its kind on the market.

But that’s a big IF.

The drug Flibanserin is locked in a heated battle for approval from the U.S. Food and Drug Administration, raising controversial questions about why there are so many sexual enhancement drugs available for men and zero for women.

Cindy Whitehead, the founder and COO of Sprout Pharmaceuticals, a Raleigh, North Carolina-based company focused on producing only Flibanserin, has been fighting for FDA approval for the drug for three years.

“There are 25 approved drugs for some form of male sexual dysfunction, but still a great big zero for the most common form of FSD [female sexual dysfunction],” Whitehead said. “No matter how or why we got here, we're here, and we've got to come up with a solution for it.”

Flibanserin is more than curing a weak libido. It’s specifically for treating Hypoactive Sexual Desire Disorder, or HSDD. Gynecologist and sexual health crusader Dr. Lauren Streicher explained that HSDD goes much deeper than just a low sex drive.

“[HSDD] is a very specific problem in a woman who doesn’t think about sex, she doesn’t fantasize, she doesn’t desire sex,” Streicher said. “What makes it different is that it’s distressing to her. This has a negative impact on her. She’s worried about it, she’s frustrated.”

According to the International Journal of Women’s Health, as many as 1 in 10 women suffer from HSDD. While many doctors agree HSDD is a problem that should be addressed, there are no medical treatment options.

Whitehead believes Flibanserin is the solution to solving female sexual dysfunction, but said it’s not accurate to call the drug “female Viagra” because it doesn’t work in the same way that Viagra does for men.

“Viagra is a blood-flow issue, a mechanical issue, and Flibanserin works on key chemicals in the brain,” she said.

Scientists have known for years that a woman’s most significant sexual organ is actually her brain, which is what makes female desire disorders so hard to treat.

Flibanserin is taken daily at bedtime, but it’s not a hormonal supplement. Instead, the pill manipulates certain chemicals in the brain to achieve desire.

To test it in clinical trials, Whitehead said it was important to find women who genuinely suffer from HSDD, and not just boredom.

“There's a diagnostic questionnaire that physicians go through, and they really can pretty quickly get to whether or not this is a relationship dynamic or something that's happening biologically,” she said.

Amanda Parrish said that’s exactly what she was facing. A mother of four from Nashville, Tenn., Parrish said she used to have a smoldering sex life with her husband, but over time, things cooled off. She said the problem wasn’t with him, but with her.

“I felt like even though we were close and having a great relationship there was something that wasn't extremely gratifying,” Parrish said. “There was something just not there, so I was in search of something that would make that happen.”

Feeling pressure to be a so-called “wholesome soccer mom,” Parrish said she never discussed the issue with her friends but had a feeling she wasn’t alone. “If you asked ten ladies on the street I think seven or eight would fess up that their sex life is not what they wanted it to be,” she said.

After filling out a questionnaire, Parrish found out she had symptoms of HSDD and was selected to participate in the Flibanserin clinical trials. She had to take the pills every day and keep a diary of her progress.

“The diary was very personal,” Parrish said. “Every morning it would go off and I would have to answer if I had sex, if I had initiated sex, if I had turned it down, if I had lubricated, if I had orgasmed. ... Within a couple weeks I began to notice a dramatic difference in the way I responded.”

Over 1,000 women participated in Sprout’s key clinical trial. According to Sprout Pharmaceutical’s results, on average, women taking Flibanserin doubled their number of so-called “satisfying sexual events” with taking the drug, and reported a 50 percent increase in sexual desire.

But about 15 percent of those women in the clinical trials dropped out because of side effects, including sleepiness, dizziness and anxiety, which Flibanserin proponents point out seem mild compared to the side effects listed in the now iconic Viagra commercials, such as nausea, diarrhea and the risk of erections lasting over four hours.

The FDA last rejected Flibanserin in December 2013, though Whitehead and Sprout Pharmaceuticals are appealing the FDA’s decision.

“We heard from the FDA in the simplest term, ‘no,’” Whitehead said. “What they basically said to us is in the risk-benefit evaluation. They felt that Flibanserin's effect was only modest, and, therefore, they didn't give us an approval.”

The FDA’s rejection of Flibanserin ignited a storm of controversy with many crying sexism. The government agency was bombarded with letters in support of the drug from prominent women’s groups and even a handful of congresswomen.

“There’s absolutely some sexism at play,” Streicher said. “No one is making this up. This is not a hallmark holiday that someone just decided to invent something in order to sell more of something.”

The FDA declined “Nightline’s” request for an interview about Flibanserin and declined to comment on the drug, but said in a statement that they are, “committed to supporting the development of therapies for medical conditions related to female sexual dysfunction” and denied allegations of gender bias. Read the FDA's full statement here.

Some doctors believe Flibanserin was rejected for a very simple reason: it’s an ineffective drug for a non-existent problem.

Dr. Adriane Fugh-Berman, an associate professor at Georgetown University Medical Center (GUMC), is also the director of the medical center’s research project PharmedOut, which analyzes the effects of pharmaceutical marketing on prescribing practices. She said the buzz created around Flibanserin is a “classic marketing technique” for new drugs.

“It’s not sexist for the FDA not to approve a drug that it doesn’t believe is effective or safe,” Fugh-Berman said. “It’s a classic marketing technique to first create a problem, and then sell the solution, and that’s what’s going on here,”

“Of course sexual desire varies by person and it varies by phase of life, but that doesn’t make it a disease,” she continued. “This is a drug with minimal effectiveness, if any, and it’s meant to be taken every day for a condition that is not of a disease.”

At the FDA’s request, Sprout Pharmaceuticals is running two more trials on Flibanserin before the agency brings it up for review again. If Sprout wins the appeal, Flibanserin could be available with a prescription as early as next year.

“I will be the first one waiting for my prescription,” Parrish said. “I believe that strongly in how it works and that women deserve an equal opportunity to enjoy and become equal members in their sex life as men have become with the products available.”

U.S. Food and Drug Administration's Full Statement to "Nightline":

The FDA is committed to supporting the development of therapies for medical conditions related to female sexual dysfunction. The agency has approved treatments for pain during sexual intercourse and vaginal dryness associated with menopause. Additionally, the FDA has also identified female sexual dysfunction as one of 20 disease areas of high priority and focused attention. The agency will be actively soliciting patients’ perspectives on their condition and its impact on daily life.

The FDA cannot discuss any drug that is still under regulatory consideration. The agency evaluates drugs based on science and strongly rejects claims of gender bias. Currently, the FDA continues to work with the company to determine whether the drug’s benefits could outweigh its risks. The FDA strives to protect and advance all important areas of women’s health, and the agency is committed to working with companies to develop safe and effective treatments for female sexual dysfunction.