Breast cancer drug may help women with PCOS get pregnant. [Photo/IC]

A drug commonly used to treat certain types of breast cancer may be more effective as a fertility treatment than the current one preferred in women with the polycystic ovary syndrome (PCOS), according to a U.S. study published Wednesday.

PCOS is a hormone imbalance that can cause irregular periods, unwanted hair growth and acne. It affects 5 to 10 percent of reproductive-age women and is the most common cause of female infertility. For decades, clomiphine citrate, a drug that stimulates ovulation, has been the standard treatment.

"Clomiphine has its drawbacks," said Richard Legro, professor at the Penn State College of Medicine and lead author on the study in the New England Journal of Medicine.

"It's only 22 percent successful with up to six cycles of treatment in producing a successful birth, it has a high multiple- pregnancy rate in comparison to unassisted conception, and it has side effects including hot flashes and mood changes."

In the new study of 750 infertile women with PCOS, researchers compared clomiphine with another drug called letrozole, which can block estrogen production.

These women were randomly assigned to either clomiphene or letrozole and took the medications for up to five cycles, with increasing dosage each cycle.

The researchers found the group of women who received letrozole had a higher rate of live births, 27.5 percent compared with 19.1 percent in the group treated with clomiphene.