It is the small pink pill that its manufacturers hope will do for women what Viagra did for men. The decision to give the drug a marketing licence in the US has been cheered on by campaigners for women’s rights, but the question remains whether Addyi is the breakthrough medicine claimed.

Men have the blue diamond-shaped Viagra pill and 25 others (although 17 of those are forms of testosterone), while there has until now been no counterpart for women. But sex and relationship therapists say Addyi is only moderately effective, should not be taken with alcohol, and has potentially serious side-effects. Trials showed that Addyi gave women who took it daily one extra sexually satisfying experience per month.

Some of the women who testified before the US drug licensing committee, the Food and Drug Administration, seemed to believe the pill would bring back the passion and romance of times past, but there are fears they are being sold an unfulfillable dream.

“I am concerned about the expectations that women have,” said Cynthia Graham, professor in sexual and reproductive health at the University of Southampton. “Among women who spoke at the FDA, there were expectations that you can have sexual desire that is at a high level and nothing is going to affect it – that it will be right back where it was when you met your partner.”

Graham and other critics believe the FDA was pressured and half-shamed into approving Addyi (generic name flibanserin) by a campaign headed by a vocal group called Even the Score, which pitched the absence of drugs to help women with low libido as a gender inequality issue. It describes itself as a campaign for women’s sexual health equality which was “created to serve as a voice for American women who believe that it’s time to level the playing field when it comes to the treatment of women’s sexual dysfunction”. On the front page of its website now runs a banner saying “Thank you, FDA”. Sprout Pharmaceuticals, which owns Addyi, is one of the funders, as is Trimel, another company in the same field.

Sprout plans to enlarge the company. Its shareholders should be in for a windfall if the drug produces even a fraction of the success and profits Viagra did for Pfizer.

Sprout’s chief executive, however, hailed the FDA decision as a victory for women. “It has been a remarkable journey to get to this breakthrough moment. Today we celebrate what this approval means for all women who have long awaited a medical treatment option for this life impacting condition,” said Cindy Whitehead. “We applaud the FDA for putting the patient voice at the center of the conversation and for focusing on scientific evidence.”

The decision was not clear cut. The drug, an antidepressant that works on the brain, unlike Viagra, was rejected twice by the FDA on the basis of a small benefit and substantial side-effects. The final vote was 18 to 6, with none of the panel willing to endorse it without caveats. Addyi will have a black box warning, meaning there are serious side-effects. It is not approved for women past the menopause or anyone with an impaired liver. It can cause low blood pressure and loss of consciousness. Those risks are higher if women drink.

“Because of a potentially serious interaction with alcohol, treatment with Addyi will only be available through certified health care professionals and certified pharmacies,” said Dr Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research. “Patients and prescribers should fully understand the risks associated with the use of Addyi before considering treatment.”

The FDA wants Sprout to do further studies of the impact of alcohol. The one it carried out involved 25 people, of whom 23 were men. Graham believes there is little chance doctors will hold off prescribing it for women who drink or who are post-menopause. Even in the hours after the announcement of the licence “we could see signs that the drug is not going to be prescribed only to women who are pre-menopausal and don’t drink”, she said.

Dr Irwin Goldstein, who heads the San Diego sexual medicine centre and has been a consultant to Sprout, told the New York Times he would not refuse to give it to casual drinkers.

There are also questions about the true scale of unmet need. The often used statistic that more than two-fifths of all women – 43% – experience loss of sexual desire dates from a survey in 1999 which failed to ask women whether they were actually worried by that. The bigger and more recent National Attitudes and Sexual Lifestyles study in the UK found that about 10% of women had low libido and were experiencing distress as a result.

Dr Petra Boynton, an agony aunt and psychologist who has researched sexual functioning, says losing interest in sex is a real worry for women, “But what are they actually worried about? They think they are not normal because they don’t want sex that much. They wonder, ‘Will my partner leave me?’ and, ‘Am I undesirable or inadequate?’”

There are some who wonder if they are missing out on pleasure, she said, but that was not their main anxiety. “They are talking about not being good enough or not measuring up. People have a perception that everybody else is having fantastic sex all the time with exotic positions.” There is, Boynton said, “anxiety brought about by misinformation about sex”, which is perpetuated by the media and especially men’s and women’s magazines. “The cultural wallpaper is telling you that to keep someone and be desirable and not left alone, which is a huge fear, you must be having and providing frequent sex.”

Addyi could help a small number of women, but Boynton pointed out that, like the other drugs for sexual problems, it had only been tested against placebos. It would have been interesting, she said, to trial it against candles and bathnights and sex toys – and, for that matter, relationship therapy.

The drug will be on sale in the US from October. Sprout has not said whether it will apply for a licence to sell it in Europe, but if it did, the verdict might not necessarily be the same. “I would be surprised if it is licensed here,” said Boynton. “But whether it is licensed or not, it will still perpetuate the illusion that if you don’t have desire, there is something wrong with you.”

Timeline

1970 Masters and Johnson publish “Human Sexual Inadequacy”, the result of over a decade of work at the Reproductive Biology Research Foundation in St Louis. Clinical research into the causes of sexual dysfunction had begun.

1998 Viagra licensed in the USA and Europe, but rationed in the UK to men who were impotent because of physical illness only. Health secretary Frank Dobson said it would prove a serious drain on NHS resources. Pfizer stumbled across the drug when testing the chemical compound sildenafil citrate to treat high blood pressure and angina. Patients developed erections, and a blockbuster was born.

2004 Hypoactive sexual desire disorder in women is included in the psychiatrists’ bible, the Diagnostics and Statistical Manual of Mental Disorders (DSM) in the USA. It is classified as “persistently or recurrently deficient (or absent) sexual fantasies and desire for sexual activity” causing “marked distress or interpersonal difficulty”. Drug companies worked on treatments including the use of Viagra in women.

October 2010 The FDA rejects Boehringer Ingelheim’s flibanserin for female sexual disorder, saying there is little evidence it increases libido and citing unacceptable side-effects. The company sells it to Sprout.

October 2013 Second FDA rejection.

August 2015 FDA approves flibanserin, given the brand name Addyi by Sprout, but with a black box warning of side-effects.