This study is to see how well a new medicine, called **E2086**, works for adults with **narcolepsy type 1** (NT1). Narcolepsy is a condition that makes people very sleepy during the day. The study compares E2086 to a **placebo** (a fake medicine that doesn't do anything) to see if it helps people stay awake. Participants must be at least 18 years old and have a history of being very sleepy during the day. They also need to have **cataplexy**, which is when emotions like laughing or being surprised make you lose muscle control for a short time. **Key points:** - The study will use tests like the **Maintenance of Wakefulness Test (MWT)** to see if E2086 helps people stay awake. - People who join the study will need to take the medicine and have regular sleep tests. - Participants must not have any major heart problems, recent COVID-19 exposure, or be pregnant. They also cannot be using certain sleep or stimulant medications. This is a chance to help others with narcolepsy by seeing if E2086 is a good treatment!