a study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of tak-925 in healthy volunteers and participants with narcolepsy

Conditions: Healthy Participants; Narcolepsy

Summary: the purpose of this study is to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of tak-925 when administered to healthy participants and narcolepsy participants.

the drug being tested in this study is called tak-925. tak-925 is being tested in healthy participants and participants with narcolepsy. this study will look at the safety, tolerability, pharmacokinetics, and efficacy of tak-925. this study will consist of three parts. part a will be a randomized, double-blind, placebo-controlled, multiple rising dose (mrd) study in healthy participants. part b is a randomized, double-blind, placebo-controlled mrd study in participants with narcolepsy. part c is a randomized, double-blind, placebo-controlled, parallel group, multiple repeat dose study in participants with narcolepsy. part a' is a single dose study in healthy participants. the study will enroll approximately 96 participants planned as total. all participants except part a' will be randomly assigned (by chance, like flipping a coin) to one of the two treatment groups-which will remain undisclosed to the participants and study doctor during the study (unless there is an urgent medical need): part a: * tak-925 (dose levels a1-a6) * placebo part b: * tak-925 (dose levels b1-b4) * placebo part c: * tak-925 (dose levels c1-c2) * placebo part a': • tak-925 (dose levels a'1-a'2) all participants will be asked to take tak-925 or placebo at the same time each day from day 1 to day 7 in parts a, b and c, and take tak-925 on day 1 in part a'. this multi-center trial will be conducted in japan. the overall study period is approximately 15 days in parts a, b and c, and approximately 7 days for part a'. participants will be partly admitted to a hospital during the study.

Eligibility criteria:
inclusion criteria: healthy adult participants and healthy elderly participants: • participant weighs at least 50 kg (healthy adults participants) / 40 kilogram (kg) (healthy elderly participants) and has a body mass index (bmi) from 18.5 to 30 kilogram per square meter (kg/m\^2), inclusive at screening. narcolepsy participants: * participants weighs at least 40 kg inclusive at screening (\>=50 kg is required for cohort b4). * a diagnosis of narcolepsy, as defined by the international classification of sleep disorders, third edition (icsd-3). * at day -1, epworth sleepiness scale (ess) score \>=10 exclusion criteria: all participants: * participants consume excessive amounts, defined as greater than 6 servings (1 serving is approximately equivalent to 120 mg of caffeine) of coffee, tea, cola, energy drinks, or other caffeinated beverages per day. * participants have a moderate to severe substance use disorder. * participants have a risk of suicide according to endorsement of item 4 or 5 with screening/baseline visit c-ssrs (columbia suicide severity rating scale) or has made a suicide attempt in the previous 6 months. * participants have a lifetime history of major psychiatric disorder, such as bipolar disorder or schizophrenia. * participants experienced sleep wake cycle disturbance with external factors such as irregular work hours.