A Clinical Study to Examine the Drug-drug Interactions Between ACT-541468 and Citalopram in Healthy Male and Female Subjects

Inclusion Criteria: * Signed informed consent prior to any study-mandated procedure. * Healthy male and female subjects aged between 24 and 55 years (inclusive) at Screening. * Body mass index of 18.5 to 29.9 kg/m2 (inclusive) at Screening. * Women of childbearing potential must have a negative serum pregnancy test at Screening and a negative urine pregnancy test on Day -1. They must consistently and correctly use a highly effective method of contraception, be sexually inactive, or have a vasectomized partner. * Women of non-childbearing potential (i.e., postmenopausal, with previous bilateral salpingectomy, bilateral salpingo oophorectomy or hysterectomy, or with premature ovarian failure, XY genotype, Turner syndrome, uterine agenesis). * Healthy on the basis of physical examination, cardiovascular assessments, and clinical laboratory tests. Exclusion Criteria: * Pregnant or lactating women. * Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol. * Modified Swiss Narcolepsy Scale total score \< 0 at Screening or history of narcolepsy or cataplexy. * Any contraindication to citalopram or any other selective serotonin reuptake inhibitor. * History of cardiovascular disease (e.g., congenital long QT syndrome, arrhythmia). * Relevant history of a suicide attempt or suicidal behavior. * Personal or family history of psychiatric disorder(s). * Individuals of Asian descent. * History or clinical evidence of alcoholism or drug abuse within the 3-year period prior to Screening. * Excessive caffeine consumption, defined as ≥ 800 mg per day at screening. * Previous treatment with any prescribed medications (including vaccines) or over-the-counter (OTC) medications (including herbal medicines such as St John's Wort, homeopathic preparations, vitamins, and minerals) within 2 weeks or 5 terminal half-lives (t½; whichever is longer) prior to first study treatment administration. * Ongoing, recurrent, or chronic hypokalemia or hypomagnesemia.