['chronic idiopathic constipation']
['placebo', 'lubiprostone']

        Inclusion Criteria:

          1. In the opinion of the investigator, the participant is capable of understanding and
             complying with protocol requirements.

          2. The participant or, when applicable, the participant's legally acceptable
             representative signs and dates a written, informed consent form and any required
             privacy authorization prior to the initiation of any study procedures.

          3. Has a history of constipation defined as having sudden bowel movement (SBM) frequency
             of less than 3 times per week on average for 6 months or longer and for whom the SBM
             frequency is confirmed to meet inclusion criteria observed during the Screening
             Period.

          4. Has had 1 or more of the symptoms associated with SBM (described below) for 6 months
             or longer at the start of Screening:

               1. Scybalum stool or hard feces in at least 1 out of every4 bowel movements.

               2. Sensation of incomplete evacuation in at least 1 out of every 4 bowel movements.

               3. Straining in at least 1 out of every 4 bowel movements.

          5. Rarely has loose stools without the use of laxatives.

          6. Is willing and able to keep a diary on his/her own and willing and able to complete a
             questionnaire.

          7. Is male or female and aged 19 years or older, at the time of signing an informed
             consent.

          8. A female participant of childbearing potential who is sexually active agrees to use
             routinely adequate contraception from signing of informed consent throughout the
             duration of the study and 14 days after the last dose of study drug.

        Exclusion Criteria:

          1. Has received any investigational compound within 30 days prior to Screening.

          2. Has received lubiprostone in a previous clinical study or as a therapeutic agent.

          3. Is an immediate family member, study site employee, or is in a dependent relationship
             with a study site employee who is involved in conduct of this study (eg, spouse,
             parent, child, sibling) or may consent under duress.

          4. Has, in the judgment of the investigator, clinically significant abnormal
             hematological parameters of hemoglobin, hematocrit, or erythrocytes at Screening.

          5. Has a history or clinical manifestations of significant mechanical obstruction
             (intestinal obstruction due to tumor, hernia etc).

          6. Has a history of hypersensitivity or allergies to lubiprostone or any of its
             excipients.

          7. Has a history of drug abuse (defined as any illicit drug use) or a history of alcohol
             abuse within 1 year prior to the Screening Visit.

          8. Is required to take excluded medications.

          9. If female, the participant is pregnant or lactating or intending to become pregnant
             before, during, or within 1 month after participating in this study; or intending to
             donate ova during such time period.

         10. Participant whose constipation is considered to be due to drugs or to whom a
             prohibited concomitant medication has been administered.

         11. Is having chronic constipation due to a secondary cause (medications, diabetes
             mellitus, hypothyroidism, depression, etc.)

         12. Has sufficient criteria for irritable bowel syndrome (IBS) or functional defecation
             disorder.

         13. Participant whose SBM frequency is 3 or more per week.

         14. Participant whose SBM frequency has been less than 3 times per week for less than 6
             months in duration or whose symptoms associated with SBM have been present for less
             than 6 months (hard feces, sensation of incomplete evacuation, or straining).

         15. Has received treatment with a rescue medication within 24 hours prior to the first
             dose in the morning of Day 1: bisacodyl suppository, which is a standard laxative,
             glycerin enema, or any other rescue medication.

         16. Has megacolon/megarectum or has received a diagnosis of intestinal pseudo-obstruction.

         17. Has confirmed or suspected organic disorders of the large intestine (obstruction,
             stenosis, carcinoma, or inflammatory bowel disease). Organic disorders of the large
             intestine can be confirmed or ruled out using the results of enema X-ray examination
             or total colonoscopy performed in the previous 2 years. If the participant has no
             history or shows no current evidence of weight loss, anemia, or rectal bleeding,
             organic disorders may be ruled out based on the results of such testing performed in
             the past 3 years. Any participant in whom total colonoscopy has detected a polyp
             requiring treatment is excluded from this study. Note: Participant should not be
             screened unless at least 7 days have passed since an enema X-ray examination,
             sigmoidoscopy or total colonoscopy have been performed.

         18. Has been hospitalized for gastrointestinal or abdominal surgery within 3 months prior
             to Screening.

         19. Has a significant cardiovascular, liver, lung, kidney, neurological, or mental disease
             (including existing alcohol or drug abuse problem) or a systemic disease.

         20. Has significant clinical findings or a significant abnormality has been found in
             hematology test, serum chemistry, or urinalysis.

         21. Participant in whom noncompliance with the study protocol (administration schedule,
             visit schedule, diary completion or other study procedure) is expected.

         22. Has a history of malignant disease (except basal cell carcinoma) within 5 years prior
             to Screening.

         23. Has any screening abnormal laboratory value that suggests a clinically significant
             underlying disease or condition that may prevent the participant from entering the
             study; or the participant has: creatinine >1.5 mg/dL, alanine aminotransferase (ALT)
             and/or aspartate aminotransferase (AST) >2 times the upper limit of normal (ULN), or
             total bilirubin >2.0 mg/dL with AST/ALT elevated above the limits of normal values.

         24. Participant who the investigator/subinvestigator has determined ineligible to
             participate in this study for any reason other than the above.
      