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.
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.