Eisai Co., Ltd. (Headquarters: Tokyo, CEO: Haruo Naito, “Eisai”) announced today that it has received an orphan drug designation for its in-house discovered and developed novel selective orexin 2 receptor agonist E2086, with prospective indication for narcolepsy, from the Ministry of Health, Labour and Welfare (MHLW).

Narcolepsy is a chronic sleep disorder that is characterized by excessive daytime sleepiness (EDS). Due to problems with fatigue, cognition, and persistence of residual symptoms despite treatment, disease burden for narcolepsy is high,(1) and narcolepsy remains a disease with high unmet medical needs. While estimates vary depending on the study data, a 2025 report estimates the narcolepsy patient population in Japan to be approximately 46,000.(2) Narcolepsy is classified into two subtypes, type 1 (narcolepsy with cataplexy) and type 2 (narcolepsy without cataplexy). The pathogenesis of narcolepsy type 1 is thought to involve a deficiency of orexin due to autoimmune destruction of orexin-producing neurons located in the hypothalamus. Although the pathogenesis of narcolepsy type 2 remains unknown, it has been suggested that a reduction in orexin neurotransmission may also be involved.(3)

Orexin is a neurotransmitter that plays a central role in regulating sleep and wakefulness. Inhibiting orexinergic neurons is believed to promote a natural transition from wakefulness to sleep. Conversely, activating orexinergic neurons is believed to help maintain a more stable state of wakefulness. From the perspective of inhibiting orexinergic neuron activity, Eisai has developed the insomnia treatment DAYVIGO® (generic name: lemborexant), an orexin receptor antagonist that is approved in more than 25 countries and regions worldwide. Furthermore, leveraging the unique orexin platform established through the development of DAYVIGO, Eisai has created E2086, a selective orexin 2 receptor agonist that activates orexinergic neurons. E2086 has the potential to improve patients’ symptoms by enhancing orexin receptor activity and acting on the pathophysiology of narcolepsy. Eisai presented data from a Phase Ib clinical study in patients with narcolepsy type 1, which suggests that E2086 has the potential to improve daytime wakefulness, at the World Sleep 2025 congress.(4)

Eisai considers neurology, including sleep-wake disorders such as insomnia and narcolepsy, as a therapeutic area of focus. Eisai strives to create innovative products in therapeutic areas with high unmet medical needs as soon as possible and will further contribute to addressing the diverse needs of, as well as increasing the benefits provided to, those living with neurological diseases and their families.