This study tests a new medicine, MK-6552, to see if it's safe and works for people with Narcolepsy Type 1 (NT1). NT1 is a sleep disorder that makes people very sleepy during the day and can cause sudden muscle weakness called cataplexy. The study has two parts. In Part 1, they test different doses of the medicine on one day to find a safe amount. In Part 2, they check how the medicine works after taking it for several days. Only people who handle the medicine well in Part 1 can join Part 2. To be in the study, you need a diagnosis of NT1 and be able to sleep more than 6 hours most nights. You can't join if you have heart, kidney, or liver problems, a history of cancer, or certain other health issues.

• Part 1 lasts one day; Part 2 may last several days.
• Only join if you meet specific health criteria.
• There might be risks if you have certain health conditions.