Inclusion Criteria:

• Male or non-pregnant, non-breastfeeding female, age 18-70 years old at the time of first dose;
• Sexually active patients of childbearing potential agree to use double-barrier birth control;
• Females of childbearing potential must complete negative pregnancy tests prior to first dose;
• Negative colonoscopy within 10 years or completion of negative flexible sigmoidoscopy if under the age of 50 provided there is no history of rectal bleeding, weight loss, or anemia;
• BMI must be greater than/equal to 18.5 and less than 35.0;
• Successful completion of physical exam, 12-lead ECG, clinical laboratory tests prior to first dose of study medication;
• Vital signs must not have clinically-significant findings within 4 hours of first dose of study medication;
• Patient reports 3 or less spontaneous bowel movements (SBMs) per week and meets 1 or more of the following criteria for constipation for 12 weeks in the previous 12 months: straining at least 25% bowel movements (BMs), lumpy or hard stools at least 25% of BMs, or sensation of incomplete evacuation at least 25% of BMs;
• Patient reports 3 or less SBMs during the 7-day Pre-treatment Period;
• Patient is compliant with IVRS for at least 6 days in the 7-day Pre-treatment Period.

Exclusion Criteria:

• Use of investigational drug within 30 days;
• Laxative/enema-induced diarrhea within 60 days;
• Patient meets ROME II criteria for functional diarrhea;
• Most bothersome symptom is moderate or severe abdominal pain or abdominal discomfort;
• History of cancer, inflammatory bowel disease, ischemic colitis, bowel resection, colostomy, or fecal impaction;
• Diagnosis of cathartic colon or laxative/enema abuse, pelvic floor dysfunction, evacuation disorder, bulimia, anorexia, or neurological disorders;
• Surgery within 30 days or GI surgery within 6 months of first dose of study medication. Cholecystectomy and/or appendectomy are acceptable if completed more than 60 days prior to first dose of study medication;
• Patient may not use any disallowed medications (prescription and/or over-the-counter treatments for chronic constipation or C-IBS, drugs that target 5-HT4, 5-HT2b, or 5-HT3 receptors, narcotics, anti-cholinergic agents, GI preparations, etc.) during the 7-day Pre-treatment Period or during the study. Stable, continuous (30 days or more) use of dietary fiber is acceptable.
• Any acute or chronic condition that would limit the patient's ability to complete and/or participate in the study.