A Study to Measure Daridorexant in Breast Milk of Healthy Lactating Women

Inclusion Criteria: * Signed informed consent in a language understandable to the subject prior to any study-mandated procedure. * Healthy lactating female subject aged at least 18 years at Screening. * Female subject who has delivered a term infant (≥ 37 weeks' gestation) and who is breastfeeding her infant (and/or pumping) for at least 2 weeks postpartum at Screening; lactation must be well-established to maintain an adequate milk supply with regular breastfeeding (and/or pumping, e.g., 3 to 4 times per day and not providing more than 1 supplemental bottle of formula per day and the infant has not started eating solids). Subjects planning on weaning their infants after enrollment who meet the afore mentioned requirements will be considered for enrollment in the study. * Agreement to refrain from breastfeeding any infant with her own milk from Day -1 up to 72 h after study treatment administration. * Ability of subject's infant to feed from a bottle or no anticipated compromise of subject's infant's nutrition with time period of refraining from breastfeeding planned during the study. * Agreement to collect breast milk from pre-dose (directly prior to study treatment administration) to Day 4 (72 h after study treatment administration) using an electric pump provided by the study site. * Must agree to use an acceptable effective method of contraception consistently and correctly (e.g., oral progestin-only contraceptive; implants; intra uterine devices; male or female condom with or without spermicide; cap, diaphragm or sponge with spermicide) from Screening up to at least 72 h after study treatment administration, be sexually inactive, or be in same-sex relationship. Exclusion Criteria: * Known hypersensitivity to daridorexant or treatments of the same class, or any of its excipients. * History of narcolepsy. * Mastitis or other condition that prevents the collection of breast milk from one or both breasts at Screening or on Day -1. * History of breast implants, breast augmentation, or breast reduction surgery which prevents the collection of breast milk. * Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol.