This study is designed to evaluate the safety and effectiveness of an investigational drug, TRN-002 (crofelemer) to relieve the symptoms of diarrhea-predominant irritable bowel syndrome (IBS).

The investigational drug is a natural product taken from a plant that grows in South America. The study medication will be administered orally twice a day. Subjects who are eligible to participate will have a 75% chance of receiving TRN-002 and a 25% chance of receiving placebo (a substance that looks similar to TRN 002 but has no activity). Subjects will not be able to remain on certain standard IBS medications (antidiarrheals) while participating in the study. The total duration is 16 weeks.

The study requires five study visits that include physical exams, ECG and blood draws for laboratory studies. A colon procedure (such as a colonoscopy or flexible sigmoidoscopy) may also be required if it has not been performed since your diagnosis and within the last 5 years. Participants will be asked to make daily entries into a touch-tone telephone diary on a daily basis.

Inclusion Criteria:

• Diagnosis of diarrhea predominant Irritable Bowel Syndrome
• Willingness to make daily calls on a touch-tone telephone
• Willingness to have an endoscopic and/or radiologic bowel evaluation, if you have not received one since your IBS diagnosis and in the past 5 years
• Willingness to use an approved method of birth control

Exclusion Criteria:

• Serious medical or surgical conditions
• Gastrointestinal Cancers, Crohns Disease or Ulcerative Colitis
• Pregnancy or breast feeding