The extracted data included: (i) publication characteristics (authorship, year, country, study classification); (ii) studies that attended to the formulated PICO (Population, Intervention, Control, Outcomes) [12], which was: Population - adult narcoleptic patients without any endocrine disease, Intervention - orexin, Control - placebo or any other approved drug for the treatment, Outcomes - results of any test used to diagnose narcolepsy (Olfactory Performance Test, PSG, Sleepiness Scales, Wakefulness Maintenance Test). Here, HCRT is linked to narcolepsy.