A drug that failed as an antidepressant is finding new life as a "Viagra for women," with study results suggesting it helps boost female libido.

The drug flibanserin appears to increase sexual desire in women suffering from low sexual desire, according to the drug's German maker, Boehringer Ingelheim, which funded three clinical trials. The results were presented this week at the Congress of the European Society for Sexual Medicine in Lyon, France.

"Flibanserin was a poor antidepressant," lead researcher John Thorp, of the University of North Carolina, told the meeting. "However, astute observers noted that it increased libido in laboratory animals and human subjects... So, we conducted multiple clinical trials."

Interestingly, the drug is being dubbed "Viagra for women" after the little blue pill that treats male erectile difficulties and that was also discovered by accident. Viagra was developed as a heart medication but while it failed poorly in testing, researchers noticed it helped increase blood flow in the penis. The rest is pharmaceutical history.

Flibanserin is different from Viagra, in that is acts on the brain chemical serotonin, which is thought to play a role in sexual response, explained Elaine Jolly, a professor of obstetrics and gynecology at the University of Ottawa and one of the Canadian doctors participating in the studies.

"By modulating these neurotransmitter systems, flibanserin may help to restore a balance between inhibitory and excitatory factors leading to a healthy sexual response," she said.

For the studies, more than 2,000 women in the U.S., Canada and Europe took 100 mg of the drug once a day.

The women reported significant improvements in their sexual desire and "satisfactory sexual experiences." The women reported an average of 4.5 satisfying sexual experiences per month, compared with 3.7 women taking the placebo.

According to Boehringer Ingelheim, the drug improved sexual functioning as measured by a "Female Sexual Function Index," and relieved distress related to sexual dysfunction and low sexual desire, as measured by the "Female Sexual Distress Scale."

The most major short-term side effect from the drug was daytime sleepiness; other side effects included dizziness, anxiety, dry mouth, nausea and insomnia.

According to the drug maker, the medication relieves "hypoactive sexual desire disorder" which is marked by the persistent lack of sexual fantasies or desire for any form of sexual activity, as well as distress or interpersonal difficulty.

But some critics wonder whether female sexual dysfunction exists or if it's a symptom of other social or psychological problems. Others question whether it's an invention of the pharmaceutical industry seeking to create a disorder that requires a pill to treat it.

At the moment, the only treatment of female sexual dysfunction is a testosterone patch made by Procter & Gamble called Intrinsa. But it has only been approved in the European Union for women who have had radical hysterectomies and are taking estrogen.

Several companies are also developing testosterone sprays.