The primary objective of this study is to assess the long-term safety and effectiveness of pitolisant in patients with idiopathic hypersomnia (IH) who completed the Double-Blind Randomized Withdrawal Phase of study HBS-101-CL-010.

This is a Phase 3 open-label study to evaluate the long-term safety and effectiveness of pitolisant in adult patients with IH. Patients who complete the Double-Blind Randomized Withdrawal Phase of study HBS-101-CL-010 (i.e., completed the End-of-Treatment [EOT] Visit/Visit 5 in the HBS-101-CL-010 study) and who continue to meet eligibility criteria for study HBS-101-CL-011 are eligible for enrollment.

Enrolled patients will be dispensed open-label pitolisant and may be titrated up to a maximum dose of 35.6 mg, based on the Investigator's assessment of safety/tolerability and effectiveness, during a 3-week Titration Period (Day 1 to Day 21) in accordance with the schedule:

• Week 1 (Day 1-7), 8.9 mg
• Week 2 (Day 8-14), 17.8 mg
• Week 3 (Day 15-21), 35.6 mg

The Long-Term Dosing Period will begin on Day 22 and will continue until the patient discontinues from the study or the Sponsor elects to terminate the study (i.e., End-of-Study [EOS]).

An on-site study visit will occur approximately 180 days after Visit 2 on Day 202 (Visit 3). On-site study visits will occur approximately every 6 months and telephone contacts (TCs) approximately every one month in between until the patient withdraws from the study or the study is terminated by the Sponsor. The dose of pitolisant may be adjusted (higher or lower) in increments of 4.45 mg starting at 8.9 mg up to 35.6 mg during the Long-Term Dosing Period based on Investigator assessment of safety/tolerability and effectiveness.

All patients will receive safety follow-up TCs from the study site 15 days and 30 days after their final dose of pitolisant, to assess for adverse events (AEs) and concomitant medication use.

Inclusion Criteria:

1. Is able to provide voluntary, informed consent.
2. Completed the Double-Blind Randomized Withdrawal Phase (EOT/Visit 5) from the HBS-101-CL-010 study.
3. A patient who is a female of child-bearing potential must have a negative urine pregnancy test at the Screening Visit. A patient who is a female of child-bearing potential must agree to remain abstinent or use an effective method of non-hormonal contraception to prevent pregnancy for the duration of the study and for 21 days after final dose of study drug.
4. Must have a negative result on urine drug screen at the Screening Visit, except for medications that are prescribed by a healthcare provider for medical conditions.
5. In the opinion of the Investigator, the patient is capable of understanding and complying with the protocol and administration of oral study drug.

Exclusion Criteria:

1. Does not agree to discontinue any prohibited medication or substances listed in the protocol.
2. Is currently breastfeeding or planning to breastfeed over the course of the study. Lactating women must agree not to breastfeed for the duration of the study and for 21 days after final dose of study drug.
3. Participation in an interventional research study with an investigational medication or device, other than pitolisant, for the duration of the study.
4. Has a diagnosis of end-stage renal disease (ESRD; estimated glomerular filtration rate [eGFR] of <15 mL/minute/1.73 m2) or severe hepatic impairment (Child-Pugh C).
5. Is receiving or is unable to discontinue a medication known to prolong the QT interval.
6. Has a significant risk of committing suicide or suicidality based on history; routine psychiatric examination; Investigator's judgment; or who has an answer of "yes" on any question other than questions 1 to 3 or "yes" on any question in the suicidal behavior section of the C-SSRS, Since Last Visit.
7. Based on the judgment of the Investigator, is unsuitable for the study for any reason, including but not limited to an unstable or uncontrolled medical condition or one that might interfere with the conduct of the study, confound interpretation of study results, pose a health risk to the patient, or compromise the integrity of the study.