This is a Phase 3, multicenter, randomized, double-blind, parallel-group, placebo-controlled clinical study to assess the efficacy and safety of HBS-301 in treating idiopathic hypersomnia (IH) symptoms, including excessive daytime sleepiness (EDS), sleep inertia, and fatigue in adult participants (ages ≥18 years) with idiopathic hypersomnia (IH). The primary objective of this study is to evaluate the efficacy of HBS-301 compared with placebo in treating IH symptoms. Secondary objectives include evaluating the efficacy of HBS-301 compared with placebo in treating EDS, sleep inertia, and fatigue.