this study evaluates of the efficacy of sodium oxybate on excessive daytime sleepiness using Epworth sleepiness scale over 8 weeks compared to placebo

Bicentric, randomized, double-blind controlled study Outpatients aged from 18 to 60 years, suffering from current idiopathic hypersomnia (ICSD-3), recruited via medical consultations in the investigation centers Randomization in Xyrem or placebo arms after the inclusion visit,

1.Screening Period (up to 15 days), 2.Titration Period (up to 45 days), 3.Maintenance Period (minimum 15 days), 4.Safety Follow-Up Period (14 days)

Inclusion Criteria:

• Diagnostic of idiopathic hypersomnia (ICSD-3 criteria)
• Age between 18 and 60 years-old
• BMI between 18 and 35 kg/m2
• MSLT: mean sleep latency (MSL) ≤8 minutes and < 2 SOREMPs, AND/OR total sleep time > 11h/24h on 24-hours long-term polysomnography
• Polysomnography recording: sleep efficiency > 85%, total sleep time ≥6 hours, AHI <10/hour, micro-arousals index <15/hour, PLM index associated with micro-arousals <10/hour.
• Absence of sleep deprivation, assessed by actigraphy or sleep logs
• ESS score ≥14 points
• Written informed consent
• National health insurance cover

Exclusion Criteria:

• Current alcohol intake or treatment with modafinil, amphetamine, methylphenidate, mazindol, pitolisant, neuroleptics, sedative hypnotics, barbiturates, general anesthetics, myorelaxants, other CNS depressants, antidepressants*, anxiolytic drugs, anticonvulsive therapy, topiramate, inhibitors of GHB dehydrogenase (i.e. valproate, ethosuximide, phenytoin), budipine, dopamine antagonist antiemetics (except domperidone), opioids, benzodiazepines, Z-drugs, MAO inhibitors, COMT inhibitors, or sedative antihistamines. If patient has received such therapy, a washout-period of at least 15 days, or equivalent to 5 half-lives of the drug, prior to the inclusion in the study is required before starting treatment in this study.

  *30 days for antidepressants

• Previous intake of sodium oxybate

• Succinic semialdehyde dehydrogenase deficiency, porphyria

• Other central nervous system diseases: neurodegenerative diseases, seizure disorders or history of head trauma associated with loss of consciousness

• Lifetime history of suicide attempt or suicidal ideation in the past 6 months, prior history of psychotic episodes, current or recent history of a major depressive disorder (DSM-V), Beck depression inventory (BDI) > 16 and/or item G> 0

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

• Malignant neoplastic disease requiring therapy within 12 months prior to Visit 1 or clinically relevant

• Heart failure, severe hypertension or other cardiovascular disease compromising the patient's wellbeing or ability to participate in this study

• Renal or hepatic impairment Compromised respiratory function

• Sleep-related breathing disorders (AHI ≥ 10/h)

• No regular sleep at night: shift work or other continuous non-disease-related life conditions

• Participation in another study of an investigational drug within the 28 days prior to Visit 1 or currently

• Hypersensitivity to any of the components of the study medication

• Pregnancy (βHCG positive) and breast-feeding