One small study, which used a dose of 2 mg slow-release melatonin at bedtime, found that 50% of participants had “shortened nocturnal sleep duration, decreased sleep drunkenness and relieved daytime sleepiness.” Other studies have shown that melatonin synchronizes the circadian rhythms, and improves the “onset, duration and quality of sleep.”

Levothyroxine
There have been some studies suggesting levothyroxine as a possible treatment for IH, especially for patients with subclinical hypothyroidism. This treatment does carry potential risks (especially for patients without hypothyroidism or subclinical hypothroidism), which include cardiac arrhythmia. Hypocretin agonists
Hypocretin-1 has been shown to be strongly wake-promoting in animal models, but it does not cross the blood-brain barrier. Suvorexant, a hypocretin receptor antagonist, has been developed to limit the natural effects of hypocretin in patients with insomnia. It is therefore possible that a hypocretin agonist may be similarly developed for the treatment of hypersomnia. Acetylcholinesterase inhibitor
Antidepressants seems to have some therapeutic effects as they enhance synaptic levels of noradrenaline and serotonin and for same reason enhancing the levels of acetylcholine may have some therapeutic effect. Donepezil showed improvement in one patient by decreasing ESS score from 20 up to 14. Memantine has also shown some positive effect on a patient with narcolepsy. Levodopa
Levodopa is an amino acid and is the precursor to the neurotransmitters dopamine, norepinephrine (noradrenaline), and epinephrine (adrenaline).
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. "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.