Kat Fu, M.S., M.S.

Dual orexin receptor antagonists (DORAs) and Z-drugs like Ambien work through fundamentally different mechanisms. Z-drugs amplify GABA — the brain’s inhibitory molecule — to force sedation. DORAs block orexin receptors to reduce the brain’s wake drive, allowing sleep to occur without forced sedation. This difference explains why people on DORAs report sleep that “feels more

Orexin neuron activity responds to glucose, leptin, ghrelin, light exposure, exercise, and meal timing. Rising blood glucose and leptin (satiety) suppress orexin firing. Ghrelin (hunger) and exercise activate it. The suprachiasmatic nucleus uses light input to gate when orexin fires on a circadian schedule. These are not abstract mechanisms — they translate to practical decisions

“Wired but tired” is not a personality trait or a stress response that resolves with relaxation techniques. It is a measurable brain state. Orexin neurons in the lateral hypothalamus are activated by corticotropin-releasing hormone (CRH) — the molecule that initiates the stress response. Chronic stress keeps orexin firing into the night, overriding sleep pressure. PET

Melatonin and orexin work as opposing forces in the brain’s sleep-wake regulation. Melatonin, released by the pineal gland under circadian control, inhibits orexin neurons in the lateral hypothalamus via MT1 receptors. When melatonin rises in the evening, it suppresses orexin — opening the sleep window. When melatonin is weak or mistimed and orexin remains active,

Orexin neuron count declines with age — postmortem studies show approximately 10% fewer orexin-immunoreactive neurons in older adults compared with younger adults. At the same time, the remaining orexin neurons become hyperexcitable due to ion channel impairment, lowering the threshold for sleep-to-wake transitions. Combined with age-related circadian amplitude dampening, these changes explain why sleep fragments

Orexin is a neuropeptide produced by a cluster of neurons in the lateral hypothalamus. Its primary role is stabilizing wakefulness — not just promoting it, but preventing the brain from falling into sleep during the day. The suprachiasmatic nucleus controls when orexin neurons fire, creating a circadian gate. When that gate malfunctions — from aging,