Study of TAK-925 in Participants With Obstructive Sleep Apnea (OSA) Who Are Experiencing Excessive Daytime Sleepiness (EDS) Despite Adequate Use of Continuous Positive Airway Pressure (CPAP)

Inclusion Criteria:

• Has OSA diagnosed according to the international classification of sleep disorders-3 (ICSD-3) criteria and with current use of CPAP.

• Has a complaint of EDS despite "consistent use" of CPAP as defined by machine trackingtime as having at least 4 hours of CPAP use/night on at least 70% during theapproximately 1 month before randomization.

• If taking a stimulant medication for the treatment of excessive daytime sleepinessmust be willing to discontinue medication before randomization into the study.

• Has a regular bedtime between 21:00 and 24:00 as verified by history and regular timein bed averaging between 7.5 and 9.0 hours/night and gets at least 6.5 hours/night onaverage of sleep, as defined by approximately 7 days of actigraphy supported by asleep diary, which are completed at least 1 week before Study Day-2.

• Has a Epworth sleepiness scale (ESS) score of ≥10 at screening and Study Day -2, withor without stimulants.

• Nocturnal polysomnography (NPSG) demonstrates that the participant does not have othercomorbid sleep disorders or clinically significant nocturnal hypoxemia (O2 saturation ≤80% for ≥5% of total sleep time) and that their apnea-hypopnea index (AHI) is ≤10.

• Has an average (of 4 sessions) baseline MWT sleep latency less than or equal to 20minutes and no single session has a sleep latency of greater than 30 minutes asdetermined by the site investigator.

Exclusion Criteria:

• Has supine or standing average systolic blood pressure (SBP) ≥140 millimeters ofmercury (mm Hg) or average diastolic blood pressure (DBP) ≥90 mm Hg at screening orStudy Day-2; blood pressures will be averaged over 3 readings done 10 minutes (min)apart.

• A screening electrocardiogram (ECG) reveals a QT interval with Fridericia correctionmethod >450 milliseconds (ms) (men) or >470 ms (women).

• Has a usual bedtime later than 01:00 or an occupation requiring nighttime shift workor variable shift work within the past 6 months or travel with significant jet lagwithin 14 days before Study Day-2.

• Short sleepers with chronic sleep deprivation who get on average less than 7.5hours/night time in bed and/or less than 6.5 hours of sleep per night as defined byapproximately 1 week of nocturnal actigraphy testing and supported by a sleep diary,both of which are completed at least 1 week before Study Day -2 admission to theclinical unit.

• Has a history of a sleep disorder other than OSA that is associated with EDS on thebasis of interviews at the screening visit, such as, for example, restless legssyndrome, confirmed by prior pretreatment polysomnography (PSG) data demonstratingperiodic limb movement during sleep (PLMS) >15.

• Has used any over-the-counter (OTC) or prescription medications with stimulatingproperties within 7 days before dosing or 5 half-lives (whichever is longer) thatcould affect the evaluation of EDS or any use of sodium oxybate within 3 months ofscreening.

• Has nicotine dependence that is likely to have an effect on sleep (e.g., a participantwho routinely awakens at night to smoke) or challenge the conduct of this study (smokes ≥10 cigarettes/day) and/or the participant is unwilling to discontinue allsmoking and nicotine use during the study.

• Has a caffeine consumption of more than 600 mg/day for 7 days before Study Day-1 (1serving of coffee is approximately equivalent to 120 mg of caffeine).

• History or presence of any acutely unstable medical condition, behavioral orpsychiatric disorder (including active suicidal ideation), or surgical history thatcould affect the safety of the subject or interfere with study efficacy, safety, PKassessments, or the ability of the subject to complete the study per the judgment ofthe investigator.