This is a study to evaluate the safety, tolerability, and pharmacokinetics of single oral doses of TS-142 compared to placebo and of a single repeated dose compared to placebo in healthy volunteers. This Phase I study is composed of two parts; Part A (Single Ascending Dose) and Part B (Repeated Dose). The study employs a randomized, double-blind, placebo-controlled, parallel group design to evaluate the single and repeat-dose safety and pharmacokinetics of TS-142 in healthy participants.

Inclusion Criteria:

• Healthy adult male and female participants between 18 and 55 years of age, inclusive
• Body weight ≥ 45 kg at screening and admission visits.
• Body Mass Index (BMI) ≥ 18 and ≤ 30 kg/m^2 at screening visit.

Exclusion Criteria:

• Clinically significant abnormal values for hematology, clinical chemistry or urinalysis at the screening and/or admission visits.
• Clinically significant abnormal physical examination (including neurological assessments), vital signs, or 12-lead ECGs at the screening and/or admission visits.
• QTcF >450 msec for male participants or QTcF >470 msec for female participants at the screening and/or admission visits.
• Significant history or presence of hepatic, renal, cardiovascular, pulmonary, gastrointestinal, hematological, neurological, immunologic, ophthalmologic, metabolic or oncological disease.
• History or present diagnosis of sleep disorders.
• Currently experiencing sleep disturbance related to postmenopausal symptoms at the screening and/or admission visits.
• History or presence of suicidal behavior, defined as participants who have answered 'YES' to any of the C-SSRS suicidal behavior questions at the screening and/or admission visits.
• Positive urine screen for alcohol or controlled substances at the screening or admission visits.
• Recent history (within the previous 6 months) of alcohol or drug abuse.
• Regular alcohol consumption of > 2 units/day or 10 units/week during the last 3 months prior to screening. One unit is equivalent to 8 g of alcohol: a half pint (240 mL) of beer, a glass (125 mL) of wine, or 25 mL of spirits.
• Current use, or use of tobacco or tobacco-containing products (cigarettes, pipes, e-cigarettes, nicotine patches, etc.) during the month prior to screening, or positive urine cotinine screen (>400 ng/mL) at the screening and/or admission visits.
• History of and/or current evidence of serologic positive results for hepatitis B surface antigen (HBsAg), hepatitis C antibodies, or human immunodeficiency virus (HIV) antibodies 1 and 2.
• Donation of one or more units of blood, plasma (including platelet donations), or acute loss of an equivalent amount of blood within 60 days prior to screening visit (one unit= 450 mL).
• Exposure to any investigational product within 60 days prior to screening.
• Use of any prescription or over-the-counter medication, herbal medication, vitamins, or mineral supplements within 14 days prior to administration of the study drug.
• Participants who regularly consume >500 mg of caffeine on a daily basis.
• Is known to be allergic to the study drug or any components of the study drug.
• Participated in strenuous exercise within 48 hours prior to study start (initial dosing) and/or is unwilling to avoid strenuous exercise at any time throughout the study.
• Participants who work night shifts or need to work night shifts during the trial.