Idiopathic hypersomnia (IH) is a neurological disorder which is characterized primarily by excessive sleep and excessive daytime sleepiness (EDS).Narcolepsy and hypersomnia: review and classification of 642 personally observed cases. Roth B. Schweiz Arch Neurol Neurochir Psychiatr. 1976;119(1):31-4 Idiopathic hypersomnia was first described by Bedrich Roth in 1956, and it can be divided into two forms: polysymptomatic and monosymptomatic. The condition typically becomes evident in early adulthood and most patients diagnosed with IH will have had the disorder for many years prior to their diagnosis. , an FDA-approved medication exists for IH called Xywav, which is an oral solution of calcium, magnesium, potassium, and sodium oxybates; in addition to several off-label treatments (primarily FDA-approved narcolepsy medications).
Idiopathic hypersomnia may also be referred to as IH, IHS, or primary hypersomnia, and belongs to a group of sleep disorders known as central hypersomnias, central disorders of hypersomnolence, or hypersomnia of brain origin. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) defines idiopathic hypersomnia as EDS without narcolepsy or the associated features of other sleep disorders. It occurs in the absence of medical problems or sleep disruptions, such as sleep apnea, that can cause secondary hypersomnia. It is relatively common for mood disorders (depression or bipolar disorder) to occur at the same time as IH, with a small increase in anxiety disorder diagnoses. Chee, M. W. L., Baumert, M., Scott, H., Cellini, N., Goldstein, C., Baron, K., Imtiaz, S. A., Penzel, T., & Kushida, C. A. (2025). World Sleep Society recommendations for the use of wearable consumer health trackers that monitor sleep. Sleep Medicine, 131, 106506. https://doi.org/10.1016/j.sleep.2025.106506
Signs and symptoms Individuals with IH share common symptoms including excessive daytime sleepiness, sleep inertia, brain fog, and long sleep periods.
Excessive daytime sleepiness, characterized by persistent sleepiness throughout the day and often a general lack of energy, even during the day after apparently adequate or even prolonged nighttime sleep. People with EDS nap repeatedly throughout the day and have strong urges to sleep while driving, working, eating, or conversing with others. Sleep inertia (also known as sleep drunkenness), characterized by having extreme difficulty waking up and feeling an uncontrollable desire to go back to sleep. Clouding of consciousness characterized by inattention, thought process abnormalities, comprehension abnormalities, and language abnormalities. These symptoms may affect performance on perception, memory, learning, executive functions, language, constructive abilities, voluntary motor control, attention, and mental speed. Affected individuals can complain of forgetfulness, confusion, or inability to think clearly. Excessive sleep (9 hours or more over a full 24-hour period), without feeling refreshed after waking. Daytime naps can be up to several hours and are also unrefreshing.
Some studies have shown increased frequencies of palpitations, digestive problems, difficulty with body temperature regulation, and other symptoms in patients with IH. Anxiety and depression are frequent, and are likely to be a response to chronic illness. A case series in 2010 found that peripheral vascular symptoms, such as cold hands and feet (e.g., Raynaud syndrome), were more common in people with IH than in controls.
Other autonomic dysfunctional symptoms, such as fainting episodes, dizziness upon arising, possibly migrainous headaches, food cravings, and impotence may also be correlated with IH. Researchers have found that people reporting IH symptoms report high levels of autonomic dysfunction on par with other conditions of autonomic failure (i.e., MSA and diabetes). there is no evidence that such symptoms are related to IH.
Causes Unlike narcolepsy with cataplexy, which has a known cause (autoimmune destruction of hypocretin-producing neurons), the cause of IH is largely unknown. , researchers have identified a few abnormalities associated with IH, which with further study may help to clarify the etiology.
Destruction of noradrenergic neurons has produced hypersomnia in experimental animal studies, and injury to adrenergic neurons has also been shown to lead to hypersomnia. IH has also been associated with a malfunction of the norepinephrine system and decreased cerebrospinal fluid (CSF) histamine levels.
Researchers have recently found an abnormal hypersensitivity to GABA (the major brain chemical responsible for sedation) in a subset of patients with central hypersomnia i.e.: IH, narcolepsy without cataplexy and long sleepers. They have identified a small (500 to 3000 daltons) naturally occurring bioactive substance (most likely a peptide as it is trypsin-sensitive) in the CSF of affected patients. Although this substance requires further identification of its chemical structure, it is currently referred to as a "somnogen" because it has been shown to cause hyper-reactivity of GABAA receptors, which leads to increased sedation or somnolence. In essence, it is as though these patients are chronically sedated with a benzodiazepine (medication which acts through the GABA system) such as midazolam or alprazolam, even though they do not take these medications.
Diagnosis Idiopathic hypersomnia lacks a clearly defining biological marker (e.g., HLA-DQB1*0602 genotype in narcolepsy). Doctors can more carefully exclude these causes of EDS in order to more correctly diagnose IH. However, "even in the presence of other specific causes of hypersomnia, one should carefully assess the contribution of these etiological factors to the complaint of EDS and when specific treatments of these conditions fail to suppress EDS, the additional diagnosis of IH should be considered." IH remains underrecognized and frequently misdiagnosed. Shahzadi, M., Monderer, R., & Thorpy, M. J. (2025). Understanding idiopathic hypersomnia: Diagnosis, pathophysiology, and management. Current Opinion in Pulmonary Medicine, 31(6), 597–604. https://doi.org/10.1097/MCP.0000000000001221
The severity of EDS can be quantified by subjective scales, such as the Epworth Sleepiness Scale and the Stanford Sleepiness Scale, and also by objective tests, like actigraphy, psychomotor vigilance task, maintenance of wakefulness test (MWT), multiple sleep latency test (MSLT) although as per latest research studies, the effectiveness of MSLT has been called into question. Several groups of researchers have found normal MSLT results in patients who otherwise seem to have IH. Therefore, when IH is suspected, researchers suggest appending a 24-hour continuous polysomnography to the standard overnight/MSLT study in order to record total sleep time.
The recent studies have also found that reports of sleepiness in IH relate more to mental fatigue rather than physiological sleepiness per se and the subjective scales like ESS, IH symptom diary (IHSD) and PGIC better captures the severity of symptoms consistently.
It is also important to note that whereas narcolepsy is strongly associated with the HLA-DQB1*0602 genotype, "HLA typing is of no help in the positive diagnosis of idiopathic hypersomnia." This is "despite some reports that suggest an increase [sic] frequency of HLA Cw2 and DRS in idiopathic hypersomnia subjects."
In patients with IH, polysomnography typically shows short sleep latency, increased mean slow wave sleep, and a high mean sleep efficiency. "Latency to REM sleep and percentages of light sleep and REM sleep were normal, compared with normal ranges." Despite this, one study has found increased sleep fragmentation in patients with IH without long sleep time, suggesting multiple possible presentations.
Per ICSD-3, five criteria must be met for a diagnosis of IH:
Daytime lapses into sleep or an irrepressible need to sleep on a daily basis, for at least 3 months Absence of insufficient sleep syndrome Absence of cataplexy Absence of other causes of hypersomnia The presence of positive MSLT tests.
The latest ICD-10 defines IH with long sleep time as a neurological disorder that is a rare sleep disorder characterized by prolonged sleep at night and extreme sleepiness during the day. There are no apparent causes. This disorder affects the ability to function. It is of central nervous system origin characterized by prolonged nocturnal sleep and periods of daytime drowsiness. Affected individuals experience difficulty with awakening in the morning and may have associated sleep drunkenness, automatic behaviors, and memory disturbances. This condition differs from narcolepsy in that daytime sleep periods are longer, there is no association with cataplexy, and the multiple sleep latency onset test does not record sleep-onset rapid eye movement sleep.
Management Since the underlying mechanism is not yet fully understood, treatment efforts have usually focused on symptom management. In August 2021, low-sodium oxybate (Xywav) became the first U.S. FDA-approved treatment for idiopathic hypersomnia. Wake-promoting medications used in narcolepsy are also commonly used off-label to help manage the excessive daytime sleepiness of IH. Stimulants tend to be less effective for IH than they are for narcolepsy and may be less well tolerated.
Stimulants The main treatment of excessive daytime sleepiness is done through central nervous system stimulants. However, no stimulant medication has received FDA or EMA approval for the treatment of EDS in IH. As such, stimulants are used off-label in the treatment of IH.
Modafinil and armodafinil are non-amphetamine wake-promoting agents often used in the treatment of IH. They are thought to work by binding to the dopamine transporter, thereby inhibiting dopamine reuptake and increasing its availability. Modafinil can cause uncomfortable side effects, including nausea, headache, and a dry mouth for some patients, while other patients report no noticeable improvement even on relatively high dosages. They may also "interact with low-dose contraceptives, potentially reducing efficacy, although the scientific data supporting this claim is weak and rests on poorly documented anecdotes."
Methylphenidate and dextroamphetamine are psychostimulants with long histories of use in the treatment of hypersomnolence. Increased extracellular dopamine availability is thought to be the main property explaining wake-promotion from these medications, although effects on norepinephrine also likely contribute. Insomnia is another common side effect and may require additional treatment.
Solriamfetol is a dopamine and norepinephrine reuptake inhibitor (NDRI) used to treat excessive daytime sleepiness associated with narcolepsy and obstructive sleep apnea.
Pitolisant, a selective histamine 3 (H3) receptor antagonist/inverse agonist. It works by increasing the synthesis and release of histamine, a wake-promoting neurotransmitter in the brain.
Sleep-promoting medications Sodium oxybate (Xyrem) is an orphan drug which was designed specifically for the treatment of narcolepsy. Common side effects include nausea, dizziness, and hallucinations. A 2016 study by Leu-Semenescu et al. found sodium oxybate reduced daytime sleepiness in IH to the same degree as in patients with narcolepsy type 1, and the drug improved severe sleep inertia in 71% of the hypersomnia patients. In July 2020, the FDA approved Xywav™ (calcium, magnesium, potassium, and sodium oxybates), an oral solution for the treatment of cataplexy or excessive daytime sleepiness (EDS) in patients 7 years of age and older with narcolepsy.
Cognitive behavioral therapy