Study to Assess Safety and Efficacy of Tenapanor for Treatment of IBS-C in Pediatric Patients 12 to Less Than 18 Years

Inclusion Criteria: * ≥12 and \<18 years old * Patient weighs ≥18 kg at the time the patient provides written assent * Females of child-bearing potential must have negative pregnancy test at Visit 1 (serum) and Visit 2 (urine) and confirm the use of appropriate contraception (including abstinence). * Patient meets the Rome IV criteria for child/adolescent diagnosis of IBS-C * Patient is willing to discontinue any laxatives used in favor of the protocol-permitted rescue medicine (which will only be allowed after 72 hours with no bowel movement) * Patient meets the entry criteria assessed during the 2-week Screening period. * Ability of both the patient and parent/guardian/LAR to communicate with the Investigator and to comply with the requirements of the entire study, including an understanding of the assessments in the eDiary and how to use the eDiary device * Patient must provide written assent and the parent/guardian/LAR must provide written informed consent before the initiation of any study-specific procedures Exclusion Criteria: * Functional diarrhea as defined by Rome IV child/adolescent criteria * IBS with diarrhea (IBS-D), mixed IBS (IBS-M), or unsubtyped IBS as defined by Rome IV child/adolescent criteria * History of non-retentive fecal incontinence. * Required manual disimpaction any time prior to randomization (after consent); * Has both unexplained and clinically significant alarm symptoms (lower gastrointestinal \[GI\] bleeding \[rectal bleeding or heme-posit…