Young women with low libido had good sex more often after using a testosterone spray, Australian researchers said on Thursday.

The spray, designed by Australian group Acrux Ltd. and being developed by U.S.-based Vivus Inc., has previously worked on women who have passed menopause, who typically have low testosterone levels.

However, investigators said the company may be able to win approval for its product more easily by targeting young women, in whom the spray would bring testosterone back to normal levels.

“This is a very different ball game. It’s a different market,” said head investigator Susan Davis, the chair of women’s health at Monash University.

There is currently no available treatment to help women with low sex drive, and analysts have estimated a successful therapy could snare sales of more than $1 billion a year.

Acrux’s MDTS spray was tested over four months in three different doses on 261 young women with low libido and low testosterone levels. The number of satisfying sexual experiences they had in the final month was compared with a baseline number set a month before the trial.

Researchers found a statistically significant rise in the number of satisfying experiences at the end of the fourth month for women taking the second highest dose of the spray compared with those taking a placebo.

“In the most effective treatment group, the number of satisfactory sexual events more than doubled at week 16, compared with the baseline,” the company said.

The only side effect of the MDTS spray was a small increase in hair growth, which prompted two women in the highest dose group to drop out of the study.

The women’s sex spray was likely to take at least two or three more years to get to market, Davis said.

Vivus is working with the U.S. Food & Drug Administration to design final stage trials for the drug.

“Vivus will have to make a decision whether they want to pursue the work in pre-menopausal women,” Davis told Reuters.

She said by targeting younger women the company might meet less resistance with U.S. regulators than Procter & Gamble had with its Intrinsa testosterone patch, which the drug giant wanted to use to treat low sex drive in post-menopausal women.

An FDA advisory panel recommended in December against approving the patch, saying longer-term safety data are needed.

“I think people are very uncomfortable about treating older women with hormones to achieve levels that are perhaps normal for young women,” Davis said. Giving a young woman testosterone to restore it to the same levels as other normal young women is a very different concept.