A Study of TAK-861 for the Treatment of Selected Central Hypersomnia Conditions

Inclusion criteria:

1. Participant with a diagnosis of NT1 who has completed a controlled trial with TAK-861, and for whom the investigator has no clinical objection to their enrollment.

Exclusion criteria:

1. Participant has a treatment-emergent adverse event (TEAE) that remains severe at thetime of rollover related to the trial intervention from the parent trial ordiscontinued because of TEAEs in the parent trial.

2. Participant has a risk of suicide according to endorsement of item 4 or 5 on theColumbia Suicide Severity Rating Scale (C-SSRS).

3. The participant has alanine aminotransferase (ALT) and aspartate aminotransferase (AST) values greater than (>) 1.5 times the upper limit of normal (ULN).

4. Participant has a current medical disorder, other than narcolepsy with or withoutcataplexy, associated with excessive daytime sleepiness (EDS).

5. Participant has current active major depressive episode (MDE) or has had an activeMDE in the past 6 months.

6. Participant has developed (within the last 6 months) gastrointestinal disease thatis expected to influence the absorption of drugs.

7. Participant has epilepsy or history of seizure.

8. Participant has any other medical condition, such as anxiety, depression, heartdisease, or significant hepatic, pulmonary, or renal disease, that requires them totake excluded medications.

9. Participant has a history of cerebral ischemia, transient ischemic attack (less than (<) 5 years ago), or cerebral hemorrhage.

10. Participant has a history of myocardial infarction, clinically significant coronaryartery disease, clinically significant angina, clinically significant cardiac rhythmabnormality, or heart failure.

11. Participant has a history of cancer in the past 5 years.