Inclusion criteria:

1. Female aged 18-65 years old inclusive
2. A previous diagnosis of IBS according to Rome III criteria( ) to include those patients who have had recurrent abdominal pain or discomfort for the at least the six months prior to diagnosis and currently at least three days per month in the last three months associated with two or more of the following : a. improvement with defecation b. onset associated with a change in the frequency of stool c. onset associated with a change in form (appearance) of stool
3. Constipation predominant type IBS as defined by one or more of the following : a. fewer than three spontaneous complete bowel movements per week b. hard or lumpy stools more than 25 % of the time c. straining during a bowel movement more than 25 % of the time
4. A normal rectal exam result on file within the past two years or performed at screen to exclude the possibility of an evacuation disorder. Examination must exclude findings suggestive of an evacuation disorder such as high sphincter tone at rest, failure of perineal descent by more than one centimeter on straining and last, spasm, tenderness or paradoxical contraction of the puborectalis muscles.
5. Females of child bearing potential (those who have not experienced a bilateral tubal ligation, hysterectomy or menopause) must use an acceptable method of contraception during the study. Acceptable methods are surgical sterilization, hormonal methods such as oral contraceptives, Norplant and Depo-Provera, double barrier method such as a condom and spermicide, and an IUD. Abstinent females may participate if they agree to use the double barrier method should they become sexually active during the study.
6. Able to provide written informed consent prior to any study procedures being performed.

Exclusion Criteria:

1. Female patients who are pregnant or breast-feeding.
2. Structural or metabolic diseases/conditions that affect the gastrointestinal system, or functional gastrointestinal disorders other than C-IBS.
3. Unable to withdraw medications 48 hours prior to the study: any medication that alters GI transit including but not limited to laxatives, magnesium or aluminum-containing antacids, prokinetics, erythromycin, narcotics, anticholinergics, tricyclic antidepressants and SNRIs; analgesic drugs including opiates, NSAIDs, and COX 2 inhibitors (Note: Tylenol is permitted), GABAergic agents and benzodiazepines. Note: All other concomitant medications will be reviewed on a case by case basis by the study physicians.
4. Clinical evidence (including but not limited to a clinically significant abnormal physical exam, ECG or laboratory result in the past medical record) or current clinically significant abnormal physical exam or laboratory test result that could indicate significant cardiovascular, respiratory, renal, hepatic, gastrointestinal, hematological, neurological, psychiatric, or other diseases that interfere with the objectives of the study. If a laboratory test result is abnormal and clinically significant, it may be repeated once at the discretion of the PI. If the laboratory test result remains abnormal and clinically significant, the patient will be referred to a primary care physician for further evaluation.
5. Patients who are considered by the Investigator to be alcoholics not in remission or known substance abusers.
6. Patients who have participated in another clinical study within the past 30 days.