Since it was launched 10 years ago, more than 1.8 billion Viagra pills have been sold all over the globe, making manufacturer Pfizer one of the most profitable corporations in the world.
It was a biomedical revolution, one that led a witty urologist to describe the little blue pill as the Coca-Cola of erectile dysfunction.
Not surprisingly, the race is on to find an equivalent for women suffering from hypoactive sexual desire disorder (HSDD), which is believed to affect one third of women in America.
Women suffering from the condition do not harbour sexual fantasies or thoughts, have a very low libido and are not responsive to sexual activity.
In Singapore, urologist Peter Lim estimates that the condition affects 50 per cent of women between the ages of 28 and 60.
There have been several attempts to come up with a Viagra equivalent, but the search is proving difficult.
Pfizer, for one, actually tested Viagra on several thousand women for eight years as a potential treatment for sexual arousal disorders.
Since the sildenafil in the pill works by allowing increased blood flow to the male sexual organ, researchers theorised that it may also cause the erectile tissue of the clitoris to engorge.
The results, however, proved mixed and inconclusive. For many women, there was no increased desire for or enjoyment of sex.
The trials were abandoned in 2004.
Ms Anita Clayton, a professor at the University of Virginia's Centre for Psychiatric Clinical Research, says: 'What we know is that very little of what's going on with women and sex is below the waist. Almost all of it is above the neck.'
Researchers are now trying to come up with a drug which acts on the central nervous system or the pleasure centres of the brain.
In 2005, a lot of buzz surrounded PT-141. The drug - administered via nasal spray - was found to sexually arouse both men and women.
However the American Food And Drug Administration (FDA) stopped trials over concerns that it resulted in high blood pressure.
The FDA also nipped in the bud attempts to launch Intrinsa, which transmitted testosterone - to kick-start the libido - through a patch.
In fact, the FDA's stringent approval standards are one reason why a pink Viagra has yet to materialise.
It insists that a drug for women must not only elicit desire, but also result in an increased number of 'sexually satisfying events', a condition which drug manufacturers say is extremely vague and hard to define.
Several reasons could be behind the cautious approach.
One is a powerful lobby comprising academics, psychologists, public health advocates and feminists who feel that a woman's sexuality should not be medicalised. They are outraged that a woman who is not interested in sex should be made to feel that she has a medical problem.
But those championing the search for a pink Viagra point to several studies which show that most women distressed by their sex lives are too embarrassed to tell their doctors.
Those who do, they say, are often told to see a psychologist instead.
Another reason could be caution about side effects, fuelled by the belated realisation that hormone replacement therapy, used for years to offset the effects of menopause, was linked to a significant increase in heart disease, breast cancer and strokes.
Meanwhile, other test drugs have also made headlines.
One is LibiGel, a testosterone-laden ointment being tested at the University of Virginia.
Made by drug manufacturer BioSante, it is rubbed on the upper arms once a day. Testosterone is released into the skin over a few months.
The gel is now in clinical trials and is predicted to come before the FDA for approval within the next two years.
The other is Flibanserin, developed by a German pharmaceutical company. Originally tested as an anti-depressant, it was found to boost a woman's sexual desire instead.
Housewife Shirley Yang, 60, who has been married to a businessman for more than 30 years, is all for a pink Viagra.
But it should not merely increase a woman's libido, she says.
'Let's face it, when a woman ages, her body changes and her sexual drive changes,' she says.
'Sex can become uncomfortable because of dryness. If a drug comes along that helps to improve lubrication and libido, I'm all for it.'
This article was first published in The Straits Times on May 3, 2008.
