**Study Objective**: This research aims to understand how a medicine called *pitolisant* helps people with Prader-Willi Syndrome (PWS), a genetic condition, especially with their excessive daytime sleepiness (EDS). *Pitolisant* is tested to see if it makes people feel less sleepy during the day, and also if it helps with behaviors like irritability, eating too much (hyperphagia), and other social and behavioral issues. **Study Details**: Participants will have a period of up to 45 days to get ready (Screening/Baseline Period). Then, they will be divided into two groups: one group receives *pitolisant* and the other a placebo (a pill without medicine). This phase lasts 77 days with check-ins on Days 29, 57, and 77. After this, there's an optional phase where everyone can try *pitolisant* until Day 441, with more visits on Days 113, 260, and 441. **Key Points**: - **Length**: Up to 441 days with multiple visits. - **Eligibility**: Must have PWS, be 6 or older, and have a caregiver to help. - **Risks**: Cannot have uncontrolled sleep apnea or be in another study.

Note: Participants must be able to take oral medicine.