The U.S. Food and Drug Administration (FDA) has not given its approval to the female sex drive drug developed by Sprout Pharmaceuticals, saying it needed more data on how it interacts with other medicines and how it affects driving ability.

The agency's decision, however, did not go well with women's groups that have lobbied for the approval of flibanserin, a treatment for women who suffer from hypoactive sexual desire disorder (HSDD) or lack sexual desire.

Terry O'Neill, president of the National Organization for Women, said that the agency is gender bias. "When it comes to approving drugs for male sexual dysfunction, the FDA says yes with more limited research and serious side effects, but when it comes to women, their go-slow tactics are preventing us from having access to a treatment option where we make the decision in consultation with our healthcare provider," O'Neill said.

O'Neill's sentiment has been echoed in the letter sent by several women's groups including the Center for Health and Gender Equity, Jewish Women International, NOW and the National Council of Women's Organizations, to FDA head of pharmaceuticals division, Janet Woodcock, two days after their meeting with her on Jan. 28.

"We were pleased, Dr. Woodcock, with your recognition that 24 treatment options for men contrasted with an ongoing dilemma to just approve one for HSDD in women may signal gender bias, conscious or unconscious," they wrote. "We see this not only as an important unmet women's health issue, but an inflection point for the agency to ensure that similar standards are applied for drug approvals in conditions uniquely affecting women."

FDA denied the gender-bias charge saying that it employed a scientific process to evaluate whether flibanserin's benefits could outweigh its risks.

"We do not believe there has been any gender bias with regard to our review of this drug and FDA did not acknowledge gender bias at the meeting," said FDA spokeswoman Andrea Fischer. The agency rejected the drug last year because it found its effects to be modest in comparison with its side effects that include nausea, dizziness and fatigue.

On Tuesday, Sprout Pharmaceuticals announced that the agency required three more studies to test the drug's interaction with other medications and to simulate driving since almost 10 percent of the women involved in the trials reported of sleepiness.

Still, Sprout Pharmaceuticals sees this as a promising development for the approval of the drug. "We are encouraged by the FDA's response and view it as a significant step toward the approval of flibanserin," said Sprout Pharmaceuticals president and chief operating officer Cindy Whitehead. "With data in over 11,000 patients to date, we are confident that further supporting the predictable risk/benefit profile of flibanserin will result in women having the first ever treatment for the most common form of female sexual dysfunction. We are committed to working closely with the Agency to finally provide premenopausal women affected by HSDD with a medical treatment option."