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.
Who can participate
Age range
16 Years – 70 Years
Sex
ALL
See this in plain English?
AI-rewrites the medical criteria so a patient or caregiver can understand them. Always confirm with the trial site.
Inclusion criteria
. The participant has a body mass index (BMI) within the range 18 to 40 kilograms per meter square (kg/m\^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.
. The participant has greater than or equal to (≥)4 partial or complete episodes of cataplexy/week (WCR).
. 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
Questions worth asking your doctor
Bring these to your next appointment. They're a starting point for a shared conversation — not a sign you qualify or a recommendation to enrol.
1Based on my diagnosis and history, is this trial worth exploring for me — or is there a standard treatment we should try first?
2What does this trial's phase tell us about how much is already known about its safety and benefit?
3What would taking part actually involve for me — visits, tests, time, and travel?
4What are the known and possible risks or side effects I should weigh, and how would they be monitored?
5If this trial isn't the right fit, what other options or trials would you suggest I look into?
Generated to help you prepare — always confirm anything about your own eligibility and care with the study team and your doctor.
Questions for the trial coordinator
The trial coordinator is the person who runs the study day to day. These cover the practical side — logistics, costs, and what taking part would actually mean for your life. The study team confirms whether you meet the criteria; these are questions to ask, not a sign you qualify.
1What does taking part actually involve week to week — how many visits, where, and how long does each one take?
2What costs are covered by the study, and what might I have to pay for myself, including travel, parking, or time off work?
3What happens during screening, and what happens if the study team confirms I don't meet the criteria after those tests?
4Who pays for the scans, blood work, and other tests the trial requires — the study, my insurance, or me?
5How will being in the trial affect my regular care, and will my own doctor stay informed and involved?
6Can I leave the trial at any point if I change my mind, and what would happen to my care if I do?
A starting point for the conversation — always confirm anything about your own eligibility, costs, and care with the study team and your doctor.
What they're measuring
1
Change From Baseline to Week 12 in Mean Sleep Latency From the 4 Maintenance of Wakefulness Test (MWT) Wake Trials
. The participant has a current medical disorder, other than narcolepsy with cataplexy, associated with EDS.
. 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).
. The participant has current or recent (within 6 months) gastrointestinal disease that is expected to influence the absorption of drugs.
. The participant has a history of cancer in the past 5 years.
. The participant has a clinically significant history of head injury or head trauma.
. The participant has a history of epilepsy, seizure, or convulsion.
. The participant has any current unstable psychiatric disorder or current active major depressive episode (MDE) or an active MDE in the past 6 months.