The current study will investigate the safety, efficacy and pharmacokinetics of serdexmethylphenidate (SDX) compared to placebo in subjects with Idiopathic Hypersomnia (IH). The study may inform about the best dosing regimen, optimal dose range, duration of treatment, and secondary endpoints for a future Phase 3 study.

The main aim is to evaluate the effect of TAK-861 on symptoms of narcolepsy, including excessive daytime sleepiness (EDS) as measured by sleep latency from the Maintenance of Wakefulness Test (MWT).

The study will enroll approximately 60 participants and they will be randomly assigned to 3 groups (20 per group) to take one of two different doses of TAK-861 or a placebo. All the participants will receive the treatment for 8 weeks. Participants will be asked to complete some questionnaires during the study.

The drug being tested in this study is called TAK-861. TAK-861 is being tested to treat people who have narcolepsy without cataplexy [Narcolepsy Type 2 (NT2)]. This study will evaluate the efficacy, safety, and tolerability of 2 oral doses of TAK-861.

The overall time to participate in this study is approximately 18 weeks.

The main aim of this study is to see how TAK-861 works on symptoms of narcolepsy, including excessive daytime sleepiness and cataplexy. Approximately 100 participants will take part in the study.

The treatment (TAK-861 or placebo) will be administered for 8 or 12 weeks. After this treatment period the participant will have the option to participate in a separate, long- term extension study during which all participants will be treated with TAK-861.

The drug being tested in this study is called TAK-861. This study will look at the effect of TAK-861 on improvement in narcolepsy symptoms, including excessive daytime sleepiness (EDS) and number of cataplexy episodes.

Participants will be randomly assigned (by chance, like flipping a coin) to one of the five treatment groups (4 active and 1 placebo) which will remain undisclosed to the participant and study doctor during the study.

Participants will make multiple visits to the clinic during the treatment period and then will either enroll in a long-term extension study in which all participants will receive TAK-861 or have 2 final visits 7 and 28 days after last dose of study drug for follow-up assessments.

The overall time to participate in this study is up to 23 weeks.

The study is designed to look at the usefulness and safety of pitolisant or placebo for the treatment of Idiopathic Hypersomnia. Idiopathic Hypersomnia (IH) is a sleep disorder in which a person is excessively sleepy during the day and has great difficulty being awakened from sleep. The study staff nor the participants will know if they are receiving the study drug or a placebo. Participants will be male or female 18 or older with a diagnosis of Idiopathic Hypersomnia (IH). The study treatment period from screening to follow-up will last approximately 16 weeks, requiring five visits and seven telephone calls.

The study is designed to look at the usefulness and safety of SUVN-G3031 or placebo for the treatment of excessive daytime sleepiness. Study staff nor the participants will know if they are receiving a study drug or placebo. Participants will be male or female subjects 18-50 years old with a diagnosis of narcolepsy. The study will last approximately 3 to 7 weeks with 5 visits for an individual subject. Study drug will be administered as a pill.

The study is designed to look at the usefulness and safety of AXS-12 or placebo for the treatment of Narcolepsy. The open-label treatment period is 24 weeks, which will be followed by a double-blind treatment period of 4 weeks, for a total of up to 28 weeks with 13 visits. Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. Study staff nor the participants will know if they are receiving a study drug or placebo. Participants will be male or female subjects 15-75 years old with a diagnosis of narcolepsy. Study drug will be administered as a pill.

The study is designed to look at the usefulness and safety of AXS-12 or placebo for the treatment of Narcolepsy. Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. Study staff nor the participants will know if they are receiving a study drug or placebo. Participants will be male or female subjects 15-75 years old with a diagnosis of narcolepsy. The study will last approximately 28 weeks with 8 visits for an individual subject. Study drug will be administered as a pill.