This study will evaluate the safety, tolerability and pharmacodynamics of the investigational drug DDP733 in treating subjects with IBS-c. A placebo control will be utilized.

Inclusion Criteria:

• Subjects must have a history of IBS-c for at least 3 months prior to randomization as assessed using ROME criteria
• Must have had endoscopic/radiologic bowel evaluation within the past 10 years
• Must comply with completing a daily diary and be able to comply with GI transit measurements, including swallowing capsules containing small x-ray visible markers
• Female subjects cannot be pregnant, post-partum for less than 1 year or breastfeeding

Exclusion Criteria:

• Serious underlying diseases, including psychiatric disorders
• Current history of conditions affecting bowel transit
• Recent history of biochemical or structural abnormalities of the gastrointestinal tract, gastrointestinal surgery, or gastrointestinal infection
• Clinically significant abnormal examination findings or laboratory tests
• Inability to stop taking certain medications, or a planned change in medications (including herbal remedies) which could interfere with study assessments
• Use of drugs and or ethanol which may interfere with compliance of study procedures or influence study outcome
• Presence of a medical condition which could interfere with the interpretation of study data
• Significant use of nicotine or caffeine