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

Inclusion criteria

• 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

• Participant has a treatment-emergent adverse event (TEAE) that remains severe at the time of rollover related to the trial intervention from the parent trial or discontinued because of TEAEs in the parent trial.
• Participant has a risk of suicide according to endorsement of item 4 or 5 on the Columbia Suicide Severity Rating Scale (C-SSRS).
• The participant has alanine aminotransferase (ALT) and aspartate aminotransferase (AST) values greater than (>) 1.5 times the upper limit of normal (ULN).
• Participant has a current medical disorder, other than narcolepsy with or without cataplexy, associated with excessive daytime sleepiness (EDS).
• Participant has current active major depressive episode (MDE) or has had an active MDE in the past 6 months.
• Participant has developed (within the last 6 months) gastrointestinal disease that is expected to influence the absorption of drugs.
• Participant has epilepsy or history of seizure.
• Participant has any other medical condition, such as anxiety, depression, heart disease, or significant hepatic, pulmonary, or renal disease, that requires them to take excluded medications.
• Participant has a history of cerebral ischemia, transient ischemic attack (less than (\<) 5 years ago), or cerebral hemorrhage.
• Participant has a history of myocardial infarction, clinically significant coronary artery disease, clinically significant angina, clinically significant cardiac rhythm abnormality, or heart failure.
• Participant has a history of cancer in the past 5 years.