Linaclotide Safety and Efficacy in Pediatric Participants, 6 to 17 Years of Age, With Irritable Bowel Syndrome With Constipation (IBS-C) or Functional Constipation (FC)

Inclusion Criteria

• Male and female participants must be ages 6 to 17 years (FC participants) or ages 7 to 17 years (IBS-C participants) (inclusive) at the time the participant provides assent for the study and parent/guardian/legally authorized representative (LAR) has provided signed consent;
• Participant weighs ≥18 kg at the time the participant provides assent and the parent/guardian/LAR has provided signed consent;
• Participants who meet the modified Rome III criteria for Child/Adolescent FC. For at least 2 months before the Screening Visit, the participant has had 2 or fewer defecations (with each defecation occurring in the absence of any laxative, suppository, or enema use during the preceding 24 hours) in the toilet per week.

In addition, participant meets one or more of the following criteria at least once per week for at least 2 months before the screening visit:

a. History of retentive posturing or excessive volitional stool retention; b. History of painful or hard BMs; c. History of large diameter stools that may obstruct the toilet; d. Presence of a large fecal mass in the rectum; e. At least 1 episode of fecal incontinence per week

• For IBS-C participants only: Participant meets Rome III criteria for child/adolescent IBS: At least once per week for at least 2 months before the Screening Visit, the participant experienced abdominal discomfort (an uncomfortable sensation not described as pain) or pain associated with 2 or more of the following at least 25% of the time:
• Improvement with defecation;
• Onset associated with a change in frequency of stool;
• Onset associated with a change in form (appearance) of stool;
• For IBS-C participants only: Participant has an average daytime abdominal pain score of ≥ 1 (at least "a tiny bit") during the 14 days before Visit 3;
• Participant is willing to discontinue any laxatives used before the Preintervention Visit in favor of the protocol- permitted rescue medicine;
• Participant has an average of fewer than 3 SBMs per week during the 14 days before the randomization day and up to the randomization (including the morning eDiary assessments reported before administration of first dose of double-blind study intervention on the randomization day). An SBM is defined as a BM that occurs in the absence of laxative, enema, or suppository use on the calendar day of the BM or the calendar day before the BM;
• Participant or parent/guardian/LAR or caregiver is compliant with eDiary requirements by completing both the morning and evening assessments for 10 out of the 14 days immediately preceding the Randomization Visit;
• Female participants of childbearing potential must have a negative serum pregnancy test at the Screening Visit and a negative urine pregnancy test at the Randomization Visit prior to dosing;
• Female participants who have had their first menstrual period and are sexually active must agree to use a reliable form of contraception;
• Participant must provide written or verbal informed assent and the parent/guardian/LAR and caregiver must provide written informed consent before the initiation of any study-specific procedures;
• Participant is able to read and/or understand the assessments in the eDiary device. If the participant is 6 to 11 years of age (FC participants) or 7 to 11 years of age (IBS-C participants) and does not meet this criterion, the interviewer-administered version of the eDiary must be used and the parent/guardian/LAR or caregiver who will be administering the interviewer-administered version of the eDiary must undergo training;
• Participant must have acquired toilet training skills.

Exclusion Criteria

• For FC participants only: Participant meets Rome III criteria for Child/Adolescent IBS: At least once per week for at least 2 months before the Screening Visit, the participant has experienced abdominal discomfort (an uncomfortable sensation not described as pain) or pain associated with 2 or more of the following at least 25% of