Low Sodium Oxybate in Patients With Idiopathic Hypersomnia

Inclusion Criteria:

1. Primary diagnosis of IH, according to ICSD-3 criteria (does not require MSLT)

2. Subjects aged 18 - 65 years

3. BMI between 18 and 35 kg/m2

4. Self-reported sleep duration ≥ 9 hours most days including daytime naps/sleep basedupon at least 10/14 days of completed sleep diary entries

5. Epworth Sleepiness Scale (ESS) ≥ 10 (required at pre-screening visit only)

6. Recommended LSO by a clinical sleep specialist as part of routine medical care. Theclinical sleep specialist will be responsible for titrating LSO according tostandard of care.

7. Subject must be willing to postpone LSO therapy until all baseline assessmentscompleted

8. If treated with wake promoting agents, traditional stimulants and/orantidepressant(s), a stable dose and regimen will be required for at least 2 monthsbefore study entry and throughout the main study

9. Have used a medically acceptable method of contraception for at least 2 fullmenstrual cycles before participating in this study and consent to use a medicallyacceptable method of contraception from the first dose of study drug, throughout theentire study period, and for 30 days after the last dose of study drug.

Exclusion Criteria:

1. Succinic semialdehyde dehydrogenase deficiency, porphyria

2. Other central nervous system diseases: neurodegenerative diseases, , seizuredisorders or history of head trauma associated with loss of consciousness

3. Lifetime history of suicide attempt or suicidal ideation in the past six months,including answer to question #9 on PHQ-9 ≥1; PHQ-9 total score > 10; prior historyof psychotic episodes; active major depressive disorder

4. Change to psychiatric medication(s)/stimulant(s) within last 3 months

5. History of chronic alcohol or drug abuse within the prior 12 months

6. Malignant neoplastic disease requiring therapy within the prior 12 months

7. Heart failure, severe hypertension or other cardiovascular disease compromising thepatient's well-being or ability to participate in this study

8. Renal or hepatic impairment

9. Compromised respiratory function (e.g., history of COPD, pulmonary hypertension,and/or poorly controlled asthma)

10. Diagnosis of sleep-related breathing disorders (AHI ≥ 15 events/h using 4 % AHI) orhigh suspicion for sleep disordered breathing

11. Any sleep apnea treatment (e.g., Positive Airway Pressure (PAP) therapy, oralappliance therapy, etc.)

12. No regular sleep at night: shift work or other continuous, non-disease-related lifeconditions

13. Participation in another study of an investigational drug within the 28 days priorto Screening visit or currently

14. Pregnant and/or breast-feeding

15. Ear jewelry and/or piercings that subject not willing to/unable to remove

16. Use of device/implant that may interfere with the study devices/procedures (e.g.,vagal nerve stimulator)

17. Smoke and/or use of smokeless tobacco products

18. Subjects who, in the opinion of the investigator(s), may not be suitable for thestudy