After three applications, ownership by two drug companies, and one successful lobbying campaign, the female sexual-dysfunction drug flibanserin was approved yesterday by the Food and Drug Administration.

Flibanserin, which will be sold under the brand name Addyi, has been billed as a remedy for women with Hypoactive Sexual Desire Disorder, defined as “persistently or recurrently deficient (or absent) sexual fantasies and desire for sexual activity” in either gender.

It’s also been rejected twice, for concerns that lingered even after an FDA advisory committee voted 18-6 in June to recommend approval. The drug has an effectiveness rate of somewhere between 8 and 13 percent, and can cause side effects like fainting, dizziness, and low blood pressure, many of which were found to be exacerbated by alcohol and hormonal contraception. When it comes to market in October, Addyi’s label will carry a warning that it can’t be taken with alcohol.  (And in the alcohol-safety study submitted to the FDA, oddly, 23 of the 25 participants were men, meaning the effects of drinking while on the drug still aren’t fully understood for the women who will be taking it.)

Even so, it’s been hailed by supporters as a step towards gender equality in a previously overlooked area. “The FDA has approved 26 drugs marketed for the treatment of male sexual dysfunctions, compared to zero [now one] to address the most common form of female sexual dysfunction,” reads the website for Even the Score, a coalition of non-profits and health-care companies—including Sprout Pharmaceuticals, which makes flibanserin—that formed in 2013 to lobby for the drug’s approval.

None of those 26 drugs, though, has the same purpose as flibanserin. Viagra and its ilk enhance physical arousal; despite its nickname as the “pink Viagra,” flibanserin was developed to enhance desire. Viagra is taken before sex and increases blood flow to the genitals; flibanserin is supposed to be taken daily and aims further north, changing the balance of neurotransmitters in the brain.

The comparisons to Viagra, and the bumpy road to approval, have raised complicated questions about the nature of female desire, sexism in drug research, and what ought to qualify as a disorder.

The drug’s approval has also raised a simpler question: What changed, exactly, between those two rejections and last night?

The most obvious answer is good public relations. Even the Score, which launched in 2013, has framed the issue as one of “women’s sexual health equity.” The group notes on its site that the World Health Organization considers “[pursuit of] a satisfying, safe and pleasurable sexual life” to be a human right, and has successfully solicited letters of support to the FDA from the editor of The Journal of Sexual Medicine, the president of the National Organization for Women, and members of Congress.

In an June editorial in the Journal of the American Medical Association, three members of the FDA’s June advisory committee wrote of Even the Score: “Although flibanserin is not the first product to be supported by a consumer advocacy group [that is] in turn supported by pharmaceutical manufacturers, claims of gender bias regarding the FDA’s regulation have been particularly noteworthy, as have the extent of advocacy efforts.”

But there’s another answer, too: Between the two rejections and the approval, the benchmark for success has changed.

A highlights-only timeline of the drug’s rocky history looks like this: Flibanserin was originally developed as an antidepressant. After initial trials found it to be ineffective, it was redirected as a remedy for low female desire. The pharmaceutical company Boehringer Ingelheim submitted the drug for approval in 2010, though the agency rejected the application, noting that it didn’t seem to work very well for its new purpose, either. Sprout acquired the drug in 2011 and saw another rejection in 2013; this time, the FDA asked for additional safety studies and called for an advisory committee to investigate whether the risks outweighed the modest benefits.

Boehringer Ingelheim’s first two trials, submitted as part of the application the FDA rejected in 2010, had asked participants to keep a daily digital diary, reporting both the number of “satisfying sexual events” and the highest level of sexual desire they experienced each day. These measures were the study’s primary endpoints, or the main questions a drug trial is designed to answer. Of the two, only the number of satisfying sexual experiences slightly increased with the use of flibanserin; the pill failed to make any meaningful difference on self-reported levels of desire.

Put another way, people were having more sex—more good sex, even—but flibanserin wasn’t doing what it was supposed to do: make people want sex more in the first place.

But in a move that would later become key to flibanserin’s approval, the studies also had a secondary endpoint: how the women scored on the Female Sexual Function Index (FSFI), a tool that assigns respondents a sexual-function score based on their sexual activity over the month leading up to the survey. Unlike the digital diaries, the FSFI asked participants to recall desire from the past four weeks, rather than the past day. Also unlike with the digital diaries, this measure showed a difference between flibanserin and placebos.

When Sprout took over the development of flibanserin from BI in 2011, it conducted one more efficacy study of its own, but reshuffled the criteria. The new trial kept the number of satisfying sexual experiences as one primary endpoint, but this time around, participants weren’t asked to record their daily levels of desire; instead, the study used the FSFI—which had previously shown favorable results—as its other main measure.

Meanwhile, outside of the FDA, Sprout, and Even the Score, a third thing has changed: Hypoactive Sexual Desire Disorder (HSDD), the condition that flibanserin was developed to treat, is no longer listed by the American Psychiatric Association as its own disorder.

At the time that Spout acquired flibanersin, the most recent edition of the DSM was the DSM-IV, which drew a distinction between problems with female desire and problems with arousal. HSDD was its own entry; separately, Female Sexual Arousal Disorder was defined as “persistent or recurrent inability to attain, or to maintain until completion of the sexual activity, an adequate lubrication swelling response of sexual excitement.”

But in the DSM-V, published in 2013, the two were combined into one condition, “Female Sexual Interest/Arousal Disorder.”

“Research suggests that sexual response is not always a linear, uniform process,” the APA wrote in an explanation of the changes, “and that the distinction between certain phases (e.g., desire and arousal) may be artificial”— a change that complicates the already-complicated arguments for and against the little pink pill.