The drug works directly on the brain's pleasure zones
A drug that failed tests as an antidepressant is being hailed as "Viagra for women" after surprising but not unpleasant side effects.
In three separate trials, the drug flibanserin did wonders for women's flagging sex drive despite doing nothing to lift mood.
The accidental discovery is akin to Viagra's - it was originally designed as a heart medicine but failed.
The US work was presented at a sexual medicine meeting in Lyon, France.
Lead researcher Professor John Thorp, of the University of North Carolina, told the European Society for Sexual Medicine: "Flibanserin was a poor antidepressant.
"However, astute observers noted that it increased libido in laboratory animals and human subjects.
"So, we conducted multiple clinical trials."
The women in the studies who took 100mg of the drug once a day for their low libido reported significant improvements in their sexual desire and satisfactory sexual experiences, he said.
"It's essentially a Viagra-like drug for women in that diminished desire or libido is the most common feminine sexual problem, like erectile dysfunction is in men."
The trials were funded by manufacturer Boehringer Ingelheim and involved 2,000 women in the US, Canada and Europe.
Some doctors are sceptical about the need for pills to boost female sex drive.
For some, reduced sexual interest or response may be "normal", says Professor Irwin Nazareth or University College London.
Others say relying on a pill could stop couples talking through underlying issues.
Paula Hall of Relate said: "Female loss of libido is a big problem and it is not going away. It can cause problems within a relationship and affect self-esteem.
"This research is really quite exciting for women with loving partners whose loss of libido is a physical thing. But it is not going to fix a broken relationship or help with looking after the kids or cleaning the house."