The U.S. Food and Drug Administration has approved a drug sold as Amitiza for women who suffer from irritable bowel syndrome, according to a news release.

Dr. William D. Chey of the University of Michigan said it improves all symptoms for women with the form that causes constipation, as opposed to diarrhea.

"We found that individuals who were treated with Amitiza were nearly twice as likely to experience improvement in their IBS symptoms compared to individuals who were treated with placebo," he said.

IBS, an often painful disorder of the lower intestine, affects between 10 to 15 percent of the U.S. population, the release said.

After one week on the drug, 20 percent of the people in the study that compared the drug to a placebo reported moderate to significant relief of symptoms. The drug was only tested on women because the majority of patients are women, Chey said.

By week 4, 32 percent said they experienced relief of symptoms such as abdominal pain, bloating and constipation severity.