A Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of TAK-994 in Healthy Participants

The drug being tested in this study is called TAK-994. TAK-994 is being tested to find a safe and well-tolerated dose in healthy participants (non-Japanese and Japanese) and healthy elderly participants. The study will enroll up to approximately 160 healthy participants. The study consists of 6 parts and up to 20 cohorts as mentioned below. * TAK-994: Part A: Single-rising dose (SRD) design to assess the safety, tolerability, and PK of TAK-994 and effect of food on the PK of the TAK-994 * TAK-994: Part B: MRD design to assess the safety, tolerability, PK and PD of TAK-994 * TAK-994: Part C: MRD design to assess the safety, tolerability, PK and PD of TAK-994 and also central nervous system penetration relative to plasma concentrations of TAK-994 * TAK-994: Part D: MRD design to assess the safety, tolerability, PK and PD of TAK-994 for HE participants * TAK-994: Part E: SRD and MRD design to assess the safety, tolerability, PK and PD of TAK-994 for Japanese origin participants * TAK-994: Part F (Optional Cohort): Nonrandomized design to assess orexin (OX) levels in the cerebrospinal fluid (CSF) of untreated healthy adult participants. Participants in each cohort will be randomized to receive treatment with TAK-994 or matching placebo which will remain undisclosed to the participant and study doctor during the study (unless there is an urgent medical need). Participants in optional Part F will receive no study drug. This multi-center trial will be conducted in the United States. The overall duration of the study is approximately 10 months. Participants will be followed up for 7 days after the last dose of study drug for a follow-up assessment.