A Study of TAK-861 in People With Narcolepsy Type 1

A Randomized, Double-Blind, Placebo-Controlled Study to Evaluate the Efficacy and Safety of TAK-861 for the Treatment of Narcolepsy With Cataplexy (Narcolepsy Type 1)

The main aim of this study is to learn how effective TAK-861 is in improving excessive sleepiness during the day (called excessive daytime sleepiness or EDS) after 3 months of treatment. Other aims are to learn how effective TAK-861 is in lowering the number of sudden, unexpected attacks of muscle weakness while staying conscious (cataplexy) in a week; to learn the effect TAK-861 has on participants' ability to maintain attention, participant's overall quality of life, the spectrum of narcolepsy symptoms and daily life functions; and to learn about the safety of TAK-861.

The drug being tested in this study is called TAK-861. TAK-861 is being tested to evaluate its efficacy and safety in participants with narcolepsy with cataplexy (narcolepsy type 1 [NT1]).

The study will enroll approximately 93 participants. Participants will be randomly assigned (by chance, like flipping a coin) to one of the two treatment groups:

1. TAK-861
2. Placebo

The study drug will be administered for 12 weeks. This multi-center trial will be conducted globally.

Inclusion Criteria:

1. The participant has a body mass index (BMI) within the range 18 to 40 kilograms per meter square (kg/m^2).
2. The participant has an International Classification of Sleep Disorders, Third Edition (ICSD-3) or International Classification of Sleep Disorders, Third Edition, Text Revision (ICSD-3-TR) diagnosis of NT1.
3. The participant has greater than or equal to (≥)4 partial or complete episodes of cataplexy/week (WCR).
4. The participant is positive for the human leukocyte antigen (HLA) genotype HLA-DQB1*06:02 or results from radioimmunoassay indicate the participant's cerebrospinal fluid (CSF) orexin (OX)/hypocretin-1 concentration is less than or equal to (≤)110 picograms per milliliter (pg/mL) [or less than one-third of the mean values obtained in normal participants within the same standardized assay].

Exclusion Criteria:

1. The participant has a current medical disorder, other than narcolepsy with cataplexy, associated with EDS.
2. The participant: (a) has a history of myocardial infarction; (b) has a history of clinically significant hepatic disease, thyroid disease, coronary artery disease, cardiac rhythm abnormality or heart failure; or (c) has any medical condition (such as unstable cardiovascular, pulmonary, renal or gastrointestinal disease).
3. The participant has current or recent (within 6 months) gastrointestinal disease that is expected to influence the absorption of drugs.
4. The participant has a history of cancer in the past 5 years.
5. The participant has a clinically significant history of head injury or head trauma.
6. The participant has a history of epilepsy, seizure, or convulsion.
7. The participant has any current unstable psychiatric disorder or current active major depressive episode (MDE) or an active MDE in the past 6 months.