Study of LX1031 in Subjects With Non-Constipating Irritable Bowel Syndrome

Inclusion Criteria:

• Males and females aged 18-70 years old

• Documented diagnosis of IBS (IBS-diarrhea or IBS-mixed) based upon Rome III criteria

• Abdominal pain/discomfort at least 2 days per week during the screening and run-inperiods

• Normal structural evaluation of the colon within 5 years prior to screening

• Ability to provide written informed consent

Exclusion Criteria:

• Inability to discontinue current drug therapy for IBS, except for bulking agents,through the duration of the study

• Use of anticholinergic antidepressants, opioid pain medications, or any drugs thataffect bowel motility

• Lactose intolerance

• Major psychological disorder

• Significant nicotine or caffeine use (>10 cigarettes and/or six 8 ounce cups of coffeeper day, respectively)