So far, ACT-541468 has been studied mainly in Caucasian subjects. The present study will bridge results obtained in Caucasian subjects to those in Japanese subjects.

Key Inclusion Criteria:

• Signed informed consent form;
• Healthy male and female subjects aged between 20 and 50 years (inclusive) at screening;
• Negative serum pregnancy tests at screening and negative urine pregnancy test at Day 1 for women of childbearing potential and agreement to use a reliable method of contraception for at least 90 days after last study drug intake;
• Body mass index (BMI) of 18.0 to 26.0 kg/m2 (inclusive) at screening;
• Healthy on the basis of physical examination, cardiovascular assessments and laboratory tests;
• Caucasian or Japanese ethnicity.

Japanese subjects only:

• must be of native Japanese descent (all parents/grandparents of Japanese descent);
• must not have been away from Japan for more than 10 years (at screening visit);
• lifestyle should not have changed significantly since relocation from Japan.

Key Exclusion Criteria:

• Any contraindication to the study treatments;
• History or clinical evidence of any disease or medical / surgical condition or treatment, which may put the subject at risk of participation in the study or may interfere with the absorption, distribution, metabolism or excretion of the study treatments;
• History of narcolepsy or cataplexy or modified Swiss narcolepsy scale total score < 0;
• Any circumstances or conditions, which, in the opinion of the investigator, may affect full participation in the study or compliance with the protocol.