What is the difference between narcolepsy and idiopathic hypersomnia?

Although narcolepsy and idiopathic hypersomnia both have excessive daytime sleepiness as a common symptom, people with idiopathic hypersomnia have no sleep-onset rapid eye movement (REM) period, naps are unrefreshing (unlike with narcolepsy) and idiopathic hypersomnia is not associated with cataplexy. Idiopathic hypersomnia can be difficult to distinguish from narcolepsy, but sleep laboratory studies can help differentiate between them.

Although amphetamines are used to treat both idiopathic hypersomnia and narcolepsy, the excessive daytime sleepiness (EDS) experienced by patients with idiopathic hypersomnia does not usually respond to stimulant treatments.