Narcolepsy Type 1 (NT1) is a sleep disorder where people feel very sleepy during the day and may suddenly lose muscle control, a condition called cataplexy. This study is looking at a new medicine called MK-6552 to see if it is safe and works well for people with NT1. The study is split into two parts. In Part 1, different doses of MK-6552 will be given in one day to find a safe dose. People who can handle the medicine will go to Part 2, where the medicine will be given over multiple days to see how the body responds.

To join, participants must have NT1 and be able to sleep at least 6 hours on most nights. They cannot have serious health problems like heart issues, high blood pressure, or a history of certain sleep disorders. They also shouldn’t have any serious conditions like cancer or mental health issues in recent years.

• The study will involve multiple visits and possibly multiple doses of the medicine.
• Participants must have a recent NT1 diagnosis and sleep study.
• Health conditions like heart problems or serious mental health issues may exclude participation.