**Study Summary** This research aims to understand how a drug called _tenapanor_ affects breast milk. Tenapanor is a medication taken by mouth to help manage certain health conditions. _Pharmacokinetics_ (PK) is a term used to describe how a drug moves through the body, including how it is absorbed and excreted. In this study, researchers will observe how tenapanor and another compound, AZ13792925, are present in the breast milk of mothers taking part in the study. Participants will take tenapanor from Day 1 to Day 4. Breast milk samples will be collected on Day 4 at different times to check the drug levels. Mothers should not feed their infants the breast milk collected during the study days until 72 hours after the last dose. **Key Points:** - The study lasts until Day 10, with a follow-up visit after the last dose. - Participants must be healthy, breastfeeding or pumping, and not weaning. - All breast milk during the study will be discarded and not given to infants. Participants need to be cautious and follow all study guidelines for the safety of both themselves and their infants.