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

The main aim is to evaluate the safety and tolerability of TAK-861 on participants with type 1 narcolepsy, who were exposed to previously tested doses of TAK-861.

The drug being tested in this study is called TAK-861. TAK-861 is being tested to treat people who have narcolepsy type 1 (NT1). This study will look at the safety of TAK-861 along with improvement in narcolepsy symptoms, including excessive daytime sleepiness (EDS) and number of cataplexy episodes.

This study was initiated in parallel with the parent phase 2 studies, TAK-861-2001 (NCT05687903) and TAK-861-2002 (NCT05687916), which included participants with NT1 and narcolepsy type 2 (NT2), respectively. This long-term extension (LTE) study enrolled participants with both diagnoses from the two phase 2 studies. As the TAK-861-2002 study did not meet prespecified criteria, all participants with NT2 have been discontinued, and this extension study will only include participants with NT1 who previously completed a parent study. Additional parent studies include all TAK-861 phase 3 studies.

The study will enroll up to 500 patients. Participants will be assigned to one of the treatment groups according to the dose assigned to them in their parent study. Similarly, participants who were previously on a placebo dose will also be assigned to one of the treatment groups randomly. All participants in the study will receive TAK-861.

Participants with NT1 will receive the following dose from the parent study:

* TAK-861 Dose 1
* TAK-861 Dose 2

This multi-center trial will be conducted worldwide. The overall time to participate in this study is up to approximately 5 years. Participants will make multiple visits to the clinic (with some visits optionally conducted by home health) and will have a follow-up assessment 4 weeks after the last dose of study drug.

Eligibility Criteria:
Inclusion criteria:

1. Participant with a diagnosis of NT1 who has completed a controlled study 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 the time of rollover related to the study drug from the parent study or discontinued because of TEAEs in the parent study.
2. Participant has a risk of suicide according to endorsement of item 4 or 5 on the Columbia Suicide Severity Rating Scale (C-SSRS).
3. The participant has alanine aminotransferase (ALT) or aspartate aminotransferase (AST) values \>1.5 times the upper limit of normal (ULN).
4. Participant has a current medical disorder, other than narcolepsy with or without cataplexy, associated with excessive daytime sleepiness (EDS).
5. Participant has current active major depressive episode (MDE) or has had an active MDE in the past 6 months.
6. Participant has developed (within the last 6 months) gastrointestinal disease that is 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, heart disease, or significant hepatic, pulmonary, or renal disease, that requires them to take excluded medications.
9. Participant has a history of cerebral ischemia, transient ischemic attack (\<5 years ago), or cerebral hemorrhage.
10. Participant has a history of myocardial infarction, clinically significant coronary artery disease, clinically significant angina, clinically significant cardiac rhythm abnormality, or heart failure.
11. Participant has a history of cancer in the past 5 years.