This study examines pitolisant, a medicine for Prader-Willi syndrome (PWS), a genetic disorder that affects many parts of the body. The study checks if pitolisant helps with excessive daytime sleepiness (EDS) in children aged 6 and older with PWS. It also looks at how pitolisant affects other problems like irritability, eating too much, and behavior issues.

Participants will have different phases: a Screening/Baseline phase of up to 45 days, a Double-Blind Treatment Period where neither doctors nor patients know who gets the real medicine or a placebo (a fake treatment), and an optional Open-Label Extension Period where all get the real medicine. Visits are needed on specific days throughout the study.

• The study involves several visits, including optional follow-up periods.
• Participants must have PWS and EDS and a caregiver to help with study tasks.
• People with uncontrolled sleep apnea or other sleep disorders can't join.